Documentation: admin-guide: update bug-hunting.rst

Documentation: admin-guide: update bug-hunting.rst

Update Documentation/admin-guide/bug-hunting.rst:

- add a small section on "Modules linked in" and their possible flags;
- delete all references to ksymoops since it is no longer applicable;
- fix spello, grammar, and punctuation;
- note that get_maintainers.pl only provides recent patchers if it is
  run inside a git tree;
- add mention of scripts/decode_stacktrace.sh;

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: greg@wind.rmcc.com
Link: https://lore.kernel.org/r/c629a9ef-3867-c3d1-f6c9-2c3b0e4ac68a@infradead.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>