Document release process and cadence

[phated]

I need to create a contributor document that outlines the release process and cadence.

[phated]

Here's a rough outline:

1. ~~Manually regenerate the docs on the release PR.~~ Auto generated as of #1777
2. Release PR is merged with a better message than the default. But DO NOT change the title of the PR because release-please 3 will break. Something like chore: Release Grain v0.4.0 - Cereal
3. ~~CI will run and publish the packaged binaries.~~
4. ~~Main branch needs to be pulled down and the npm packages must be published. #948~~
5. Change the name of the main "Grain" tag to the version + release name.
6. ~~The packaged binaries need to be tested on the various platforms.~~ Tested on every PR as of #1770
7. ~~The website needs to be updated to point at the new releases. #934~~
8. ~~Homebrew package needs to be updated to the new release. #934~~
9. The website docs need to be merged if they were waiting on release.
10. The blog post needs to be drafted & PRed.
11. The announcement tweet and email need to be drafted.
12. Usually the vscode extension needs a release.

[phated]

Additional work that was found: 12. ~~Run graindoc on stdlib with an updated version https://github.com/grain-lang/grain-lang.org/pull/289~~ 13. ~~Update website docs with the stdlib graindoc sync. #934~~

[phated]

Ideally, we'd also want to test our CI release process before trying to roll it out so we don't have the failing CI issue.

[phated]

~~Until #1408 is completed, we'll want to manually regenerate the docs on the release PR before releasing.~~

[ospencer]

I believe the bug with changing the PR title was fixed. I ran a release a few weeks ago and forgot I had a browser extension that would automatically change the title and it worked fine.