help: point to `hg help urls` in `hg help config.paths`

This seems useful to point at what people can put as value for these config.

Differential Revision: https://phab.mercurial-scm.org/D10371

mercurial/helptext/config.txt

@@ -1702,7 +1702,8 b' location of the repository. Example::'
 
 These symbolic names can be used from the command line. To pull
 from ``my_server``: :hg:`pull my_server`. To push to ``local_path``:
-:hg:`push local_path`.
+:hg:`push local_path`. You can check :hg:`help urls` for details about
+valid URLs.
 
 Options containing colons (``:``) denote sub-options that can influence
 behavior for that specific path. Example::

tests/test-help.t

@@ -1833,7 +1833,7 b' Test section lookup'
   
       These symbolic names can be used from the command line. To pull from
       "my_server": 'hg pull my_server'. To push to "local_path": 'hg push
-      local_path'.
+      local_path'. You can check 'hg help urls' for details about valid URLs.
   
       Options containing colons (":") denote sub-options that can influence
       behavior for that specific path. Example: