due: Add command line calls for 'add' and usage

due.py

@@ -71,10 +71,21 @@ def due(search_term="", relative=False):
         print(i.fancy_print(relative))
 
 if __name__ == '__main__':
+    if sys.argv[1] == "usage":
+        print("    due [-r] [TERM...]\n"
+              "      Shows all items with a t: or due: tag that match TERM. '-r' makes dates relative\n"
+              "    due add [due date] [tag] [description]\n"
+              "      Adds a task with a dated tag")
+
+        exit(0)
+
     if len(sys.argv) >= 3:
         if sys.argv[2] == "-r":
             relative = True
             del sys.argv[2]
+        elif sys.argv[2] == "add":
+            add(sys.argv[3], sys.argv[4], " ".join(sys.argv[5:]))
+            exit(0)
         else:
             relative = False
         search_term = " ".join(sys.argv[2:])