Update 'README.md'

README.md

@@ -2,4 +2,7 @@ This is a build variant with PostgreSQL including [count_bits](https://github.co
 
 There are no other differences with `static-dockerhub` setup.
 
-Look here for more information: https://git.tt-rss.org/fox/ttrss-docker-compose/src/static-dockerhub/README.md
+Look here for more information: https://git.tt-rss.org/fox/ttrss-docker-compose/src/static-dockerhub/README.md
+
+Q: How do I create functions on existing database?
+A: `docker-compose exec --user postgres db sh -c "cd /opt/count-bits ; make create_functions"`