docs: add CLI help

docs/internal/release.md

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+# Release
+
+To release a new version the following steps should be followed:
+
+1. Create a new branch from `master` i.e. `release-<next semver>`. This
+   will function as your release preparation branch.
+1. Change the `VERSION` value in `cmd/tk/main.go` to that of the
+   semver release you are going to make. Commit and push your changes.
+1. Create a PR for your release branch and get it merged into `master`.
+1. Create a `<next semver>` tag for the merge commit in `master` and
+   push it to remote.
+1. Confirm CI builds and releases the newly tagged version.