Update README.md

Author: glenn-jocher

README.md

@@ -19,7 +19,8 @@ key = ''
 secret = ''
 ```
 
-3. Search for up to `n` images, and optionally `--download`. URLs are printed to screen and downloaded images are saved in `flickr_scraper/images`.
+3. Search for up to `n` images, and optionally `--download`. URLs are printed to screen and downloaded images are saved in `flickr_scraper/images`. Note that image downloads are subject to Flickr rate limits and other limitations. See https://www.flickr.com/services/developer/api/ for full information.
+
 ```bash
 $ python3 flickr_scraper.py --search 'honeybees on flowers' --n 10 --download