Dev doc: New release process

To make a new release of beaker, follow these steps:

1. Run the tests. Always gotta run the tests.
2. Create and publish a new releases page on beakerbrowser.com.
3. Update app/package.json to the new version number.
4. Update the builtin start page to reference the new version number and its release page.
5. Commit, tag, and push. (The pushed tag will trigger appveyor's build process.)
6. Create a new release draft off of the tag.
7. Build on OSX. Add latest-mac.yml, the .dmg, and the .zip to the release draft.
8. Build on Linux. Add latest-linux.yml and the .appimage to the release draft.
9. When appveyor finishes, download latest.yml and the .exe and add them to the release draft.
10. Publish the new release.
11. Update the links on beakerbrowser.com's install page and publish.