Update user instructions for Neurogitea

[mguaypaq]

This is a documentation update following the migration from Gitolite to Neurogitea (see https://github.com/neuropoly/computers/issues/457).

This should also help with:

• https://github.com/neuropoly/computers/issues/683
• https://github.com/neuropoly/data-management/issues/310

It's not perfect but it should be good enough as a start? Eventually I'd like to:

• [ ] Revamp the admin instructions as well (currently just dumped into git-annex-admin.md).
• [ ] Add documentation about creating new repositories. (Maybe wait until after https://github.com/neuropoly/computers/pull/718 is merged.)
• [ ] Maybe add some documentation/examples about using curl and tea from the command-line? In particular I think it's currently the only way for a regular user to see if they have collaborator access on a repo.
• [ ] Figure out an .ssh/config stanza to make a shortcut for the ssh -N -L command.
• [ ] Add answers to questions that people ask in #database_mri on Slack.

[mguaypaq]

Oh yeah, and there are two in-page links that I have to fix, once I know how special characters in section headings get turned into page anchors (specifically, parentheses).

[nullnik-0]

Figure out an .ssh/config stanza to make a shortcut for the ssh -N -L command.

You could probably just adapt this from the ssh config I wrote for Yehuda, here. If you copy the Host web-gitea stanza, you'd just need to change the HostName to data.neuro.polymtl.ca, get rid of the ProxyJump, and include the earlier instructions for how to set up multiplexing (or you could get rid of the multiplexing, but it's convenient!)