doc: point to the main share-safe doc in the "mismatch" config

User should be able to find their way with that.

Differential Revision: https://phab.mercurial-scm.org/D9840

mercurial/helptext/config.txt

@@ -1976,6 +1976,9 b' Alias definitions for revsets. See :hg:`'
     tries to upgrade the share; if it fails, continue by
     respecting the share source setting
 
+    Check :hg:`help config format.use-share-safe` for details about the
+    share-safe feature.
+
 ``safe-mismatch.source-safe.warn``
     Shows a warning on operations if the shared repository does not use
     share-safe, but the source repository does.
@@ -1999,6 +2002,9 b' Alias definitions for revsets. See :hg:`'
     tries to downgrade the share to not use share-safe;
     if it fails, continue by respecting the shared source setting
 
+    Check :hg:`help config format.use-share-safe` for details about the
+    share-safe feature.
+
 ``safe-mismatch.source-not-safe.warn``
     Shows a warning on operations if the shared repository uses share-safe,
     but the source repository does not.