Add "How do I find bug or feature versions?" to doc/HACKING
We need to find bugfix versions for changes files and backports, and feature versions for specifications.
Let's document the git commands to do that.
For an example, see: https://trac.torproject.org/projects/tor/ticket/30224#comment:4
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information