add to release protocol

[franklin-feingold]

We have a release protocol that walks through how to process a BIDS release. As we have worked through this release process we have iterated and finetuned our process. Here are a few enhancements to this process.

The goal is for the release protocol to be a straight forward process.

Adding to a step:

• Step 2: changing previous version links to their RTD render rather than to GitHub
• Step 2: remove REL entries from the changelog
• Merge step 5 into step 2. This will reduce the number of release commits.
• Step 6: day of release ensure release branch most up to date
• Step 4: fix get -> git
• Step 4: prevent merges during release week, except for exceptional cases. These should be crucial to the specification and agreed upon by the BIDS maintainers. The exceptional cases can be expanded on. The initial cases: rendering of the specification is down, a crucial change affecting the entire specification
• Step 10: upload new pdf to zenodo (cc @effigies for this process)
• Step 11: sharing news of release on those identified platforms