compctld limitmem: Print maximum possible limit in case of too large limit

compctld.c

@@ -253,7 +253,7 @@ sockerror:
 				continue;
 			}
 			if (limit > total || total - limit < minuser) {
-				mprintf(fd, "-2 at least %zuM must remain available for users.", minuser / 1048576);
+				mprintf(fd, "-2 at least %zuM must remain available for users; maximum limit for computations is %zuM.", minuser / 1048576, (total - minuser) / 1048576);
 				close(fd);
 				continue;
 			}