Follow-up from "Docs: (EE Port) Environments Documentation review"

The following discussions from !10710 (merged) should be addressed:

• @eread started a discussion:

  In the following example, the job will deploy to all branches except `master`:

  Otherwise EE diverges from your suggestions in CE.

• @eread started a discussion:

    so we use `$CI_ENVIRONMENT_SLUG` to get a valid URL.

• @eread started a discussion:

  webserver (for example, NGINX) could then access and serve them.

• @eread started a discussion:

  - [Deploy Boards for your applications running on Kubernetes](../user/project/deploy_boards.md) **[PREMIUM]**