update readme

README.md

@@ -2,3 +2,19 @@
 
 Pokemon Showdown data processing, mostly for HHIRLLL's Pokemon league. Ugly as
 fuck.
+
+## Requirements
+
+- Python with sqlite
+- requests
+
+## Usage
+
+```sh
+$ ./main.py -h
+usage: hhirlstats [-h] [-v] [-c] [-Q {gametime,moves,nicknames,playtime,usage}] [replay ...]
+```
+
+Recommended to cache replays (`-c`) to save issuing requests to Showdown on every query.
+
+Run the program once with all your replays (or once for each replay), then start querying.

main.py

@@ -284,6 +284,11 @@ def main():
         if args.query:
             query(args.query, db)
         else:
+            if not args.replay:
+                parser.print_usage()
+                print(f"{APP}: error: either query or replay arguments are required")
+                sys.exit(1)
+
             for r in args.replay:
                 try:
                     replay = fetch(r, cache=args.cache)