[readme] move maintainer instructions to CONTRIBUTING.md

Author: ljharb

.github/CONTRIBUTING.md

@@ -0,0 +1,23 @@
+# Contributing
+
+## For maintainers
+
+### How to publish a new release
+
+1. On the `main` branch, bump the version number in `package.json`:
+
+    ```sh
+    npm version patch
+    ```
+
+    Instead of `patch`, use `minor` or `major` [as needed](https://semver.org/).
+
+    Note that this produces a Git commit + tag.
+
+1. Push the release commit and tag:
+
+    ```sh
+    git push && git push --tags
+    ```
+
+    Our CI then automatically publishes the new release to npm.

README.md

@@ -44,28 +44,6 @@ var endsWith = require('string.prototype.endswith');
 
 Polyfills + test suites for [`String.prototype.startsWith`](https://mths.be/startswith) and [`String.prototype.contains`](https://mths.be/contains) are available, too.
 
-## For maintainers
-
-### How to publish a new release
-
-1. On the `main` branch, bump the version number in `package.json`:
-
-    ```sh
-    npm version patch
-    ```
-
-    Instead of `patch`, use `minor` or `major` [as needed](https://semver.org/).
-
-    Note that this produces a Git commit + tag.
-
-1. Push the release commit and tag:
-
-    ```sh
-    git push && git push --tags
-    ```
-
-    Our CI then automatically publishes the new release to npm.
-
 ## Author
 
 | [![twitter/mathias](https://gravatar.com/avatar/24e08a9ea84deb17ae121074d0f17125?s=70)](https://twitter.com/mathias "Follow @mathias on Twitter") |