build: Add release process (#112)

Thought I'd document this whilst I'm doing it.

RELEASE.md

@@ -0,0 +1,13 @@
+# Release Process
+
+1. Bump the package version (example: [https://github.com/climatepolicyradar/azure-pdf-parser/pull/93](https://github.com/climatepolicyradar/azure-pdf-parser/pull/93)).
+2. Compare the most recent release to `main` (example: [https://github.com/climatepolicyradar/azure-pdf-parser/compare/v0.4.1...main](https://github.com/climatepolicyradar/azure-pdf-parser/compare/v0.4.1...main)). You'll generally do a release at the `HEAD` of `main`, but, you can do a release at any point after the last release.
+3. Tag the commit you want to do a release at (example: on `main`, do `git tag v0.4.2`).
+4. Push the tag (example: `git push origin v0.4.2`).
+5. Create a new release ([https://github.com/climatepolicyradar/azure-pdf-parser/releases/new](https://github.com/climatepolicyradar/azure-pdf-parser/releases/new)).
+6. For "Choose a tag", select your new tag, and for "Previous tag", change it from "auto" to the last release (example: `v0.4.1`).
+7. Press "Generate release notes" and verify that they're as expected.
+8. Ensure "Set as the latest release" is selected.
+9. Press "Publish release".
+
+NB: We follow SemVer.