Clarify role of environment variables for services

[astrojuanlu]

Describe the problem this improvement solves I wanted to pass some environment variables to a Docker image from a service, like this:

docker run -d -p 3000:3000 \
  -e "MB_DB_TYPE=postgres" \
  -e "MB_DB_DBNAME=metabaseappdb" \
  -e "MB_DB_PORT=5432" \
  -e "MB_DB_USER=name" \
  -e "MB_DB_PASS=password" \
  -e "MB_DB_HOST=my-database-host" \
   --name metabase metabase/metabase

and initially I was not sure how to do it, but it turns out that the "Environment variables" section is exactly what I needed, which is great! However, I wonder if we could clarify its role a bit.

On the other hand, the small bubble says

Environment variables specific to the service. Note! These are versioned, so don't use it for secrets.

As @ricklamers says,

you can use project or pipeline environment variables and "pass those through" to the service These aren't versioned so can be used for secrets

But maybe this fact could be made more prominent.