Add publishing information to contributing docs

Author: reinink

.github/CONTRIBUTING.md

@@ -0,0 +1,11 @@
+# Contributing
+
+## Publishing
+
+This section is intended only for the project maintainers.
+
+1. Increment the version number in the `package.json`, `./react/package.json` and `./vue/package.json` files.
+2. Commit and tag those changes.
+3. Push the commit and tag to GitHub.
+4. Review the draft release generated by GitHub.
+5. Publish the new release on GitHub. This will automatically trigger a GitHub action to publish these packages to NPM.