github: add PR template (grpc#8524)

Author: dfawley

.github/pull_request_template.md

@@ -0,0 +1,4 @@
+Thank you for your PR.  Please read and follow
+https://github.com/grpc/grpc-go/blob/master/CONTRIBUTING.md, especially the
+"Guidelines for Pull Requests" section, and then delete this text before
+entering your PR description.

CONTRIBUTING.md

@@ -33,17 +33,21 @@ guidelines, there may be valid reasons to do so, but it should be rare.
 
 ## Guidelines for Pull Requests
 
-How to get your contributions merged smoothly and quickly:
+Please read the following carefully to ensure your contributions can be merged
+smoothly and quickly.
+
+### PR Contents
 
 - Create **small PRs** that are narrowly focused on **addressing a single
   concern**. We often receive PRs that attempt to fix several things at the same
   time, and if one part of the PR has a problem, that will hold up the entire
   PR.
 
-- For **speculative changes**, consider opening an issue and discussing it
-  first. If you are suggesting a behavioral or API change, consider starting
-  with a [gRFC proposal](https://github.com/grpc/proposal). Many new features
-  that are not bug fixes will require cross-language agreement.
+- If your change does not address an **open issue** with an **agreed
+  resolution**, consider opening an issue and discussing it first. If you are
+  suggesting a behavioral or API change, consider starting with a [gRFC
+  proposal](https://github.com/grpc/proposal). Many new features that are not
+  bug fixes will require cross-language agreement.
 
 - If you want to fix **formatting or style**, consider whether your changes are
   an obvious improvement or might be considered a personal preference. If a
@@ -56,16 +60,6 @@ How to get your contributions merged smoothly and quickly:
   often written as "iff". Please do not make spelling correction changes unless
   you are certain they are misspellings.
 
-- Provide a good **PR description** as a record of **what** change is being made
-  and **why** it was made. Link to a GitHub issue if it exists.
-
-- Maintain a **clean commit history** and use **meaningful commit messages**.
-  PRs with messy commit histories are difficult to review and won't be merged.
-  Before sending your PR, ensure your changes are based on top of the latest
-  `upstream/master` commits, and avoid rebasing in the middle of a code review.
-  You should **never use `git push -f`** unless absolutely necessary during a
-  review, as it can interfere with GitHub's tracking of comments.
-
 - **All tests need to be passing** before your change can be merged. We
   recommend you run tests locally before creating your PR to catch breakages
   early on:
@@ -81,15 +75,80 @@ How to get your contributions merged smoothly and quickly:
   GitHub, which will trigger a GitHub Actions run that you can use to verify
   everything is passing.
 
-- If you are adding a new file, make sure it has the **copyright message**
+- Note that there are two github actions checks that need not be green:
+
+  1. We test the freshness of the generated proto code we maintain via the
+     `vet-proto` check. If the source proto files are updated, but our repo is
+     not updated, an optional checker will fail. This will be fixed by our team
+     in a separate PR and will not prevent the merge of your PR.
+
+  2. We run a checker that will fail if there is any change in dependencies of
+     an exported package via the `dependencies` check. If new dependencies are
+     added that are not appropriate, we may not accept your PR (see below).
+
+- If you are adding a **new file**, make sure it has the **copyright message**
   template at the top as a comment. You can copy the message from an existing
   file and update the year.
 
 - The grpc package should only depend on standard Go packages and a small number
   of exceptions. **If your contribution introduces new dependencies**, you will
-  need a discussion with gRPC-Go maintainers. A GitHub action check will run on
-  every PR, and will flag any transitive dependency changes from any public
-  package.
+  need a discussion with gRPC-Go maintainers.
+
+### PR Descriptions
+
+- **PR titles** should start with the name of the component being addressed, or
+  the type of change. Examples: transport, client, server, round_robin, xds,
+  cleanup, deps.
+
+- Read and follow the **guidelines for PR titles and descriptions** here:
+  https://google.github.io/eng-practices/review/developer/cl-descriptions.html
+
+  *particularly* the sections "First Line" and "Body is Informative".
+
+  Note: your PR description will be used as the git commit message in a
+  squash-and-merge if your PR is approved. We may make changes to this as
+  necessary.
+
+- **Does this PR relate to an open issue?** On the first line, please use the
+  tag `Fixes #<issue>` to ensure the issue is closed when the PR is merged. Or
+  use `Updates #<issue>` if the PR is related to an open issue, but does not fix
+  it.  Consider filing an issue if one does not already exist.
+
+- PR descriptions *must* conclude with **release notes** as follows:
+
+  ```
+  RELEASE NOTES:
+  * <component>: <summary>
+  ```
+
+  This need not match the PR title.
+
+  The summary must:
+
+  * be something that gRPC users will understand.
+
+  * clearly explain the feature being added, the issue being fixed, or the
+    behavior being changed, etc. If fixing a bug, be clear about how the bug
+    can be triggered by an end-user.
+
+  * begin with a capital letter and use complete sentences.
+
+  * be as short as possible to describe the change being made.
+
+  If a PR is *not* end-user visible -- e.g. a cleanup, testing change, or
+  github-related, use `RELEASE NOTES: n/a`.
+
+### PR Process
+
+- Please **self-review** your code changes before sending your PR.  This will
+  prevent simple, obvious errors from causing delays.
+
+- Maintain a **clean commit history** and use **meaningful commit messages**.
+  PRs with messy commit histories are difficult to review and won't be merged.
+  Before sending your PR, ensure your changes are based on top of the latest
+  `upstream/master` commits, and avoid rebasing in the middle of a code review.
+  You should **never use `git push -f`** unless absolutely necessary during a
+  review, as it can interfere with GitHub's tracking of comments.
 
 - Unless your PR is trivial, you should **expect reviewer comments** that you
   will need to address before merging. We'll label the PR as `Status: Requires
@@ -98,5 +157,3 @@ How to get your contributions merged smoothly and quickly:
   `stale`, and we will automatically close it after 7 days if we don't hear back
   from you. Please feel free to ping issues or bugs if you do not get a response
   within a week.
-
-- Exceptions to the rules can be made if there's a compelling reason to do so.