Add missing keys to extract translatable strings

README.md

@@ -225,7 +225,7 @@ FileNotFoundError: [Errno 2] No translation file found for domain: 'humanize'
 How to add new phrases to existing locale files:
 
 ```sh
-xgettext --from-code=UTF-8 -o humanize.pot -k'_' -k'N_' -k'P_:1c,2' -l python src/humanize/*.py  # extract new phrases
+xgettext --from-code=UTF-8 -o humanize.pot -k'_' -k'N_' -k'P_:1c,2' -k'NS_' -k'_ngettext' -l python src/humanize/*.py  # extract new phrases
 msgmerge -U src/humanize/locale/ru_RU/LC_MESSAGES/humanize.po humanize.pot # add them to locale files
 ```