Add a NFAA tag

According to the Hub [content policy](https://huggingface.co/content-policy), datasets like this one should have a Not for All Audiences (NFAA) tag.

This PR is adding one, please merge!

README.md

@@ -7,6 +7,7 @@ tags:
 - anime
 - girl
 - Tachie
+- not-for-all-audiences
 size_categories:
 - 10K<n<100K
 ---