Improve grammar in second paragraph.

Current docs demonstrate how to configure a database container but don't
explicitly specify that you should add additional environment variables
to the Gitea container to make it use the database. This just
demonstrates the changes required.

Signed-off-by: Dane Elwell <dane.elwell@ukfast.co.uk>

I wasn't sure about how tags work, maybe this is interesting for people with less knowledge of docker.

* Add disable registration as an environment variable

for docker

* Add REQUIRE_SIGNIN_VIEW as env var to docker

* Add variables to template

* Update docker docs

* Add info from #2286, minor fixes to YAML indentation

* Add space to make YAML valid again

* Clean up spelling, grammar, perspective, whitespace, language, markup, etc.

* import docs into main repository

Signed-off-by: Matti Ranta <matti@mdranta.net>