Add RELEASE.md to doc the release process

Add RELEASE.md to doc the release process so that when I have to go
through it next time I don't forget about anything.

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RELEASE.md

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+# Release Process
+
+## Cut Release in Git Repository
+
+- create a version bump commit and integrate it
+	- update the version in the `Cargo.toml`
+	- run `cargo build` so that the `Cargo.lock` is update
+	- `gps c` to create the commit
+	- `gps int` the version bump patch
+	- `gps pull` to make sure you have the latest state
+- copy the SHA of the integrated version bump commit, `git log`
+- tag the version bump commit with the version, e.g. `git tag 6.6.0 <coppied-sha>`
+- push tags up to remote, `git push --tags`
+- update `CHANGELOG.md` for new release
+	- `git-cl full > CHANGELOG.md`
+	- stage the changes to `CHANGELOG.md`, e.g. `git add CHANGELOG.md`
+	- commit changes to `CHANGELOG.md`, e.g. `gps c`
+	- integrate changes to `CHANGELOG.md`, `gps int`
+
+## Publish release to Homebrew
+
+- copy the SHA of the integrated version bump commit, `git log`
+- update the `Formula/git-ps-rs.rb` file to set the tag to the new tag value, and update the SHA to the copied sha
+- stage, commit, and push the change indicating `Release vX.Y.Z of git-ps-rs`
+
+## Publish release to Crates.io
+
+- `cargo publish --dry-run`
+- `cargo publish`
+
+## Update GitHub Releases
+
+This is important because it is utilized by the in-app versioning check that
+happens when a `gps pull` operation occurs. So publishing the release here is
+what will make people get notified while using `gps` that there is a newer
+version available.
+
+- go to [GitHub Releases Page](https://github.com/uptech/git-ps-rs/releases)
+- verify that everything looks as you expect prior to publishing a new release
+- click the [Draft a new release](https://github.com/uptech/git-ps-rs/releases/new) button
+- choose the tag you pushed up in the previous section
+- enter the tag name in the "Release title" field, e.g. `6.6.0`
+- copy the changes from this version in the `CHANGELOG.md` and paste them into the "Describe this release" text area
+- click the "Publish release" button
+
+## Notify Package Maintainers
+
+Notify package maintainers of new release so that they can update the packages
+they maintain on the respective platforms.
+
+- NixOS: Ali Caglayan (slack: `@Ali Caglayan`)
+- Homebrew: Drew De Ponte (slack: `@Drew`)
+- Crates.io: Drew De Ponte (slack: `@Drew`)