I ended up adding the following to ContentGenerator.pm, right at the end of the Instructor Tools (right after the Instructor Links).
if (exists $ce->{webworkURLs}{userGuide} and $ce->{webworkURLs}{userGuide} ne ""
and $authz->hasPermissions($userID, "access_instructor_tools")) {
print CGI::li(CGI::a({href=>$ce->{webworkURLs}{userGuide}}, $r->maketext("Comprehensive User Guide for PCC faculty")));
}
And then I put a line in localOverrides.conf defining:
$webworkURLs{userGuide} = "http://spot.pcc.edu/~ajordan/WeBWorKUserGuide.pdf";