Add a RELEASING.md file

Want to make sure the release process is documented somewhere.

RELEASING.md

@@ -0,0 +1,15 @@
+Release Process
+===============
+
+Wayland-rs has a CI automation for releasing all the subcrates on crates.io when a release is
+tagged. After updating the changelogs and versions.
+
+* Create a branch for the release
+* `cargo release` (install with `cargo install cargo-release`) can be used to bump versions
+  - For instance, `cargo release --no-publish --no-tag --no-push --execute patch`
+* Amend the commit to update the changelogs of any subcrates with changelog entries to have a release
+  date.
+* Create a pull request with the release. Check that there are no warnings from `publish` CI job
+  - Those will become hard errors when a release is tagged
+* Merge PR, and tag as `release-YYYY-MM-DD`, with the current date
+* When the tag is pushed, CI will run and release to crates.io