Add usage

reviews.py

@@ -17,9 +17,18 @@ COMMANDS = {
 }
 
 
+def print_usage():
+    print("Usage:")
+    print("\tmrs\t\t\tFetch files and create merge requests for them")
+    print("\tupdate-assignees\tUpdate assignees on MRs")
+    print("\tcomments\t\tFetch all comments on MRs")
+    print("\tmerge\t\t\tMerge all MRs")
+    print("\ttest\t\t\tDebugging function")
+
+
 def main():
     if len(sys.argv) < 2 or sys.argv[1] not in COMMANDS:
-        print("Invalid command")
+        print_usage()
         exit(2)
 
     COMMANDS[sys.argv[1]](SUBMISSIONS)()