Add a warning about settign a bridge in MyFamily

doc/tor.1.txt

@@ -1182,7 +1182,8 @@ is non-zero):
     their identity fingerprints or nicknames. When two servers both declare
     that they are in the same \'family', Tor clients will not use them in the
     same circuit. (Each server only needs to list the other servers in its
-    family; it doesn't need to list itself, but it won't hurt.)
+    family; it doesn't need to list itself, but it won't hurt.) Do not list
+    any bridge relay as it would compromise its concealment.
 
 **Nickname** __name__::
     Set the server's nickname to \'name'. Nicknames must be between 1 and 19