Add a comment to have_enough_path_info()

Comment only change

src/or/circuituse.c

@@ -1674,7 +1674,11 @@ circuit_launch(uint8_t purpose, int flags)
   return circuit_launch_by_extend_info(purpose, NULL, flags);
 }
 
-/* DOCDOC */
+/* Do we have enough descriptors to build paths?
+ * If need_exit is true, return 1 if we can build exit paths.
+ * (We need at least one Exit in the consensus to build exit paths.)
+ * If need_exit is false, return 0 if we can build internal paths.
+ */
 static int
 have_enough_path_info(int need_exit)
 {