Document release process

[simon360]

[simon360]

Hey, it would've been cool if I did this before I forgot the release process.

[simon360]

Process:

1. Check out a release branch, ie. git checkout master && git pull && git checkout -b release/v2.0.0-pre.5
2. Push the branch. Otherwise, lerna will throw a minor fit.
3. Run yarn release. This will update all the files and push the tags.
   Note: at this point, the packages will be built and pushed to npm.
4. Push the branch again. Open a PR.
5. When the build finishes, merge the PR.
6. Copy the changes from /CHANGELOG.md into the GitHub release: https://github.com/simon360/react-from-markup/releases/edit/YOUR_TAG_NAME_HERE