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- delete all references to ksymoops since it is no longer applicable;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 <[email protected]>
Cc: [email protected]
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jonathan Corbet <[email protected]>