Improvements for Cloud Docker topic (#4512)

* Improvements

* Fix formatting

* fix sentence

Author: shiftedreality

guides/v2.1/cloud/docker/docker-config.md

@@ -56,7 +56,7 @@ For example, the following command starts the Docker configuration generator for
 
 You must have the following software installed on your local workstation:
 
--  PHP version 7.0 or later
+-  PHP version 7.1 or later
     -  [php@7.1](https://formulae.brew.sh/formula/php@7.1)
     -  [php@7.2](https://formulae.brew.sh/formula/php@7.2)
 -  [Composer](https://getcomposer.org)
@@ -69,6 +69,20 @@ Before you begin, you must add the following hostname to your `/etc/hosts` file:
 127.0.0.1 magento2.docker
 ```
 
+Alternatively, you can run the following command to add it to the file:
+
+```bash
+echo "127.0.0.1 magento2.docker" | sudo tee -a /etc/hosts
+```
+
+### Stopping default Apache instance on Mac OS
+
+Because Mac OS provides built-in Apache service, and may occupy port `80`, you must stop the service with the following command:
+
+```bash
+sudo apachectl stop
+```
+
 #### To launch Docker:
 
 1.  Download a Magento application template from the [Magento Cloud repository](https://github.com/magento/magento-cloud). Be careful to select the branch that corresponds with the Magento version.
@@ -140,7 +154,7 @@ Continue launching your Docker environment in the default _production_ mode.
 1.  Configure and connect Varnish.
 
     ```bash
-    docker-compose run deploy magento-command config:set system/full_page_cache/caching_application 2 -l
+    docker-compose run deploy magento-command config:set system/full_page_cache/caching_application 2 --lock-env
     ```
 
 1.  Clear the cache.
@@ -212,7 +226,7 @@ The `{{site.data.var.ct}}` version 2002.0.18 and later supports developer mode.
 1.  Configure and connect Varnish.
 
     ```bash
-    docker-compose run deploy magento-command config:set system/full_page_cache/caching_application 2 -l
+    docker-compose run deploy magento-command config:set system/full_page_cache/caching_application 2 --lock-env
     ```
 
 1.  Clear the cache.
@@ -240,6 +254,7 @@ Action | Command
 Suspend containers to continue your work later | `docker-compose stop`
 Start containers from a suspended state | `docker-compose start`
 Stop the synchronization daemon | `docker-sync stop`
+Start the synchronization daemon | `docker-sync start`
 
 #### To stop and remove the Docker configuration:
 
@@ -254,3 +269,27 @@ docker-compose down -v
 ```bash
 docker-sync stop
 ```
+
+## Advanced usage
+
+### Extending docker-compose.yml configuration
+
+You can use Docker's built-in [extension mechanism](https://docs.docker.com/compose/reference/overview/#specifying-multiple-compose-files).
+
+1.  Create a `docker-compose-dev.yml` file inside your project's root directory and add the following content:
+
+    ```yaml
+    version: '2'
+    services:
+      deploy:
+        environment:
+          - ENABLE_SENDMAIL=true
+    ```
+
+    This replaces the default value of the `ENABLE_SENDMAIL` environment variable.
+
+1.  Pass both configuration files while executing your commands. For example:
+
+    ```bash
+    docker-compose -f docker-compose.yml -f docker-compose-dev.yml run deploy bash
+    ```