When using database backend: mention pg_trgm extension to address pg_trgm error

[frozenSolid]

Address sql extension error When I configured the postgresql database backend, I got the following error:

./amass enum -rf resolvers.txt -d owasp.org -config ~/.config/amass/config.yaml
panic: ERROR: operator class "gin_trgm_ops" does not exist for access method "gin" (SQLSTATE 42704) handling 005_assets_indexes.sql

The pg_trgm postgresql extension was not enabled on the database I was using. I encountered this on Ubuntu 22.04.3 LTS but I am sure others will enounter this as well.