Document the PHP version selection

README.md

@@ -2,16 +2,24 @@
 
 ## Setup
 
+First of all we need to know the major PHP version you're using for a project. You should create a file called `.env` in the root of your project and add a line like this:
+
+```
+PHP_VERSION=7.2
+```
+
+Supported versions are `7.0`, `7.1` and `7.2`.
+
 ### Install and update
 
 ```
-docker pull registry.lakedrops.com/docker/l3d
+export $(cat .env | xargs) && docker pull registry.lakedrops.com/docker/l3d:php-${PHP_VERSION}
 ```
 
 ### Start from the root of your project
 
 ```
-docker run -it -v /var/run/docker.sock:/var/run/docker.sock -v ${PWD}:/drupal -v $SSH_AUTH_SOCK:/ssh-agent -v ${HOME}/.traefik:/root/.traefik -e SSH_AUTH_SOCK=/ssh-agent -w /drupal registry.lakedrops.com/docker/l3d /usr/bin/fish
+export $(cat .env | xargs) && docker run -it -v /var/run/docker.sock:/var/run/docker.sock -v ${PWD}:/drupal -v $SSH_AUTH_SOCK:/ssh-agent -v ${HOME}/.traefik:/root/.traefik -e SSH_AUTH_SOCK=/ssh-agent -w /drupal registry.lakedrops.com/docker/l3d:php-${PHP_VERSION} /usr/bin/fish
 ```
 
 Instead of the shell `/usr/bin/shell` you could also use `/bin/sh` or `/bin/bash`.