Warn on primary_monitor_first

src/config.c

@@ -1287,7 +1287,12 @@ void add_entry(char *key, char *value)
         }
     }
 #endif
-    else
+    else if (strcmp(key, "primary_monitor_first") == 0) {
+        fprintf(stderr,
+                "tint2: deprecated config option \"%s\"\n"
+                "  Please see the documentation regarding the alternatives.\n",
+                key);
+    } else
         fprintf(stderr, "tint2: invalid option \"%s\",\n  upgrade tint2 or correct your config file\n", key);
 
     if (value1)