fix the URL matching regex with e. g. markdown links
the comment was a bit misleading (maybe it worked like that with qregexp, but doesn't anymore with qregularexpression at least).
so fixed the regex and updated the comment and tested a bit, seems to work more like expected now (i. e. doesn't match [https://foobar](https://foobar)
as a single link).
Edited by Martin Tobias Holmedahl Sandsmark