Add a new Troubleshooting section to the manual with 9 concise how-to
subsections covering uninstall/revert, Fish version requirements,
disabling logging, changing the greeting, secrets/local config, the
return sentinel gotcha, missing dependencies, Vi mode keybindings,
and minimal mode.
Renumber Viewing This Manual from Section 11 to Section 12 to place
troubleshooting before it. Update TOC and help index accordingly.
All verify-manual.py checks pass.
rootiest
