JIRA isn't fully under the OSS team's control,
and played up in the past (Dan couldn't move issues).
Since Github has project boards now, and we're paying
for private repos on github.com/silverstripe-security already anyway,
there's no reason to introduce another tool (JIRA) into our workflows.
No need to move existing issues, the JIRA board hasn't been used in a while.
Which leads to unclear ownership and status of security issues,
and is exactly the reason for this change ;)
The role moves around based on current availability.
@tractorcow has done most of the last releases,
but a separate team (headed by @dhensby) will be
responsible for 3.x releases.
There's not really much point to declaring a release maintainer,
unless there's disagreements in the core team where we need
an arbitrator. So far those conflicts have been resolved
on individual tickets (e.g. what should go into a release),
and the process for that seems to work well.
It was getting a bit lost halfway down the contributing/code instructions,
in between the detailed git instructions.
Also reordered the docs TOC for that folder by renaming the files.
