Update release process documentation

[reaperzn]

Update release process to ensure the following:

1. All PRs must be "Merge" NOT "squash and merge"**
2. All release PRs from master back to develop must be performed locally by a repo admin with push rights to the develop branch

$ git checkout develop
$ git pull
$ git merge --no-ff master
$ git push develop

Resolve any conflicts locally, and only push resolution to the develop branch.

This is to avoid merge conflicts during the release process.