Consider adding tips for resolving git index corruption on Tails workstations

[eloquence]

Describe the change

Packaging securedrop for Tails workstations (freedomofpress/securedrop#3502) -- and maybe later for Qubes admin workstations -- could let us avoid using git on Tails workstations altogether. In the meantime, admins and journalists alike are interacting with git repositories to keep their workstations up-to-date. That means they may also encounter git index corruption issues sooner or later, e.g., after an unclean shutdown. This is especially likely in the context of a live USB operating system like Tails, as USB devices can become unplugged accidentally.

As an interim measure until we switch to full packaging, I'd suggest adding at least some basic troubleshooting steps for recovering a securedrop directory to the docs. A method that has worked for me when I've encountered this issue (at least 2-3 times over the years) is to create a fresh clone, remove the broken .git directory and use the one from the new clone to replace it.

How will this impact users?

• It may simplify troubleshooting or rebuild operations for admins significantly.

Related evidence

• We've had occasional support tickets related to git index corruption on Tails workstations
• I've sporadically encountered the issue myself