Update README.md

Author: mikibakaiki

test-package/README.md

@@ -16,3 +16,5 @@
 2. Install python if you don't have. I recommend [pyenv](https://github.com/pyenv/pyenv).
 
 3. Run the command `./python generate_bw_passwords.py <number_of_passwords_you_want> <the_file_you_want_to_output_to>`
+
+**NOTE:** This script may take a while. For 100 pw, it takes about 1 minute. For 1000 pw, it takes about 10 minutes.