Added instructions on how to retrieve the category id

Commit e47a2dc omitted to change 2
occurences of the logo's old filename (mantis_logo.gif)

Fixes #14119

This function inserts the hrefs in 2 steps: 1) URLs and 2) emails.

When the string contains URLs specifying a username and/or password,
e.g. http://user@example.com/ or http://user:password@example.com/
the 2nd call to pcre_replace() processes the part of it that matches the
email address specification, resulting in broken links and text display
as well as invalid HTML generation.

This commit fixes the behavior by adding logic to distinguish URLs with
password and actual emails addresses.

Fixes #12781