Merge pull request #520 from python-discord/include-metricity-db-creation-for-local-setup

Include metricity db creation for local setup guide.

Author: kosayoda

pydis_site/apps/content/resources/guides/pydis-guides/contributing/site.md

@@ -62,6 +62,7 @@ Run the following queries to create the user and database:
 ```sql
 CREATE USER pysite WITH SUPERUSER PASSWORD 'pysite';
 CREATE DATABASE pysite WITH OWNER pysite;
+CREATE DATABASE metricity WITH OWNER pysite;
 ```
 
 Finally, enter `/q` to exit psql.