Create RELEASE.md document

[neufeldtech]

Had a conversation with @miry about the current release process and what further info we need to port from the readme to a dedicated document with release instructions.

In general, the process is similar to this:

• PREREQUISITE: Shopify employees performing releases should have their workstation configured to have their commits signed (verified). See Docs
• Prepare for the release locally.
  • Update the CHANGELOG.md with 2 changes
    1. Add a new version header at the top of the 'unreleased' section
    2. Update links at bottom of changelog
  • Update any version references in the README to point to the new version
• Commit this locally (and sign the commit) - Commit message should be something like Release 2.x.x
• Create a tag locally and sign it - git tag -s v2.x.x
• Run make test-release locally - this will run tests and final verifications
• Push the release commit to github (either through a PR, or straight to master branch if you have permissions)
• Wait for tests to turn green after the change is on the master branch (merge your PR as necessary)
• Push your local tag to github
• Goreleaser should create the release on Github via Github Actions
• Verify release notes were generated correctly
• Update Homebrew versions
  1. Update app_version string
  2. Update hashes for all versions (find the hashes in the checksums.txt from your release notes)
  3. Do a manual smoketest of installing toxiproxy via brew while in the shopify-homebrew repo locally brew install ./toxiproxy.rb --debug