Create a guide page about Docker setup in application templates

[samdark]

Description

Create a user guide for Docker in https://github.com/yiisoft/app and https://github.com/yiisoft/app-api

Things to note especially:

1. make commands usage.
2. Contents of /docker overview.
3. Each .env purpose and examples.
4. compose.yml.
5. The idea of multi-stage builds.