Check for secrets file

main.py

@@ -40,6 +40,9 @@ def get_yt_creds():
         if creds and creds.expired and creds.refresh_token:
             creds.refresh(Request())
         else:
+            if not os.path.exists(client_secrets_file):
+                print(f'Client secrets file {client_secrets_file} not found')
+                sys.exit(1)
             flow = InstalledAppFlow.from_client_secrets_file(
                 client_secrets_file, scopes
             )