man: use meaningful titles for <ulink>s

man: use meaningful titles for <ulink>s

As pointed out in https://github.com/systemd/systemd/issues/29814, we need to
use phrases are are meaningful on their own, because the man page formatter
creates a list at the bottom. With <ulink>see docs</ulink>, we end up with:
  NOTES:
    1. see docs
       https://some.url/page
    2. see docs
       https://some.url/page2
which is not very useful :(

Also, the text inside the tag should not include punctuation.

Python helper:
  from xml_helper import xml_parse
  for p in glob.glob('../man/*.xml'):
       t = xml_parse(p)
       ulinks = t.iterfind('.//ulink')
       for ulink in ulinks:
           if ulink.text is None: continue
           text = ' '.join(ulink.text.split())
           print(f'{p}: {text}')