multi-urls: document the feature

We have a feature lets make it visible to people.

Differential Revision: https://phab.mercurial-scm.org/D10453

mercurial/helptext/config.txt

@@ -1718,6 +1718,12 b' the path they point to.'
 
 The following sub-options can be defined:
 
+``multi-urls``
+   A boolean option. When enabled the value of the `[paths]` entry will be
+   parsed as a list and the alias will resolve to multiple destination. If some
+   of the list entry use the `path://` syntax, the suboption will be inherited
+   individually.
+
 ``pushurl``
    The URL to use for push operations. If not defined, the location
    defined by the path's main entry is used.

tests/test-help.t

@@ -1872,6 +1872,12 b' Test section lookup'
   
       The following sub-options can be defined:
   
+      "multi-urls"
+         A boolean option. When enabled the value of the '[paths]' entry will be
+         parsed as a list and the alias will resolve to multiple destination. If
+         some of the list entry use the 'path://' syntax, the suboption will be
+         inherited individually.
+  
       "pushurl"
          The URL to use for push operations. If not defined, the location
          defined by the path's main entry is used.