Rewrite the section on what information needs to be supplied to make
a good Problem Report. Add pointers to the new files ports/CHANGES
and ports/UPDATING. Change some occurrences of FreeBSD to &os; if
they were in the affected lines (another commit will do the remaining
ones). Suggest guidelines for the often-abused Severity and Priority
fields. Add a pointer to the categories definition file. Add the
'threads' category. Add a warning to include the tracking number on
followups to save creating new, bogus, PRs.

PR: docs/67062
Reviewed by: ceri, keramida, others
Approved by: ceri (mentor)