b/c...py: notify the user when reading STDIN

Notify the user when the script reads bytebeat code from STDIN

bytebeat_compiler.py

@@ -66,6 +66,7 @@ def rewrite_file(path: str, content: str):
 
 def read_from_file_or_stdin(path: str) -> str:
 	if path == "-":
+		print("Reading from STDIN...", flush=True)
 		return "\n".join(stdin)
 	elif exists(path):
 		return read_file(path)