Add envrc for automatic installation

.envrc

@@ -0,0 +1 @@
+source .venv/bin/activate

tlm/cli.py

@@ -51,7 +51,7 @@ def generate(length, context_window_words, filepath, gutenberg, list_gutenberg,
         corpus.extend(tokenize_text(mail_text, tokenize_opts))
 
     if not corpus:
-        raise click.UsageError("Must specify at least one of --text, --gutenberg, or --mbox for training data.")
+        raise click.UsageError("No training data provided. Must specify at least one of --filepath, --gutenberg, or --mbox.")
 
     # Train and generate
     model = TinyLanguageModel(n=context_window_words)