Added docker-compose.override.yml.dist example override file, updated README.md, added .gitignore

This prevents needing to stash or merge local file changes with each pull of the repository

.gitignore

@@ -0,0 +1 @@
+/docker-compose.override.yml

README.md

@@ -80,3 +80,9 @@ This will allow you to clear the cache by running the following command right in
 ```
 magento cache:flush
 ```
+
+## Docker Compose Override
+
+You can copy `docker-compose.override.yml.dist` to `docker-compose.override.yml` and adjust environment variables, volume mounts etc in the `docker-compose.override.yml` file to avoid losing local configuration changes when you pull changes to this repository. 
+
+Docker Compose will automatically read any of the values you define in the file. See [this link](https://docs.docker.com/compose/extends/#/understanding-multiple-compose-files) for more information about the override file. 

docker-compose.override.yml.dist

@@ -0,0 +1,14 @@
+# Mage Inferno Docker Compose Override Example (https://github.com/mageinferno/magento2-docker-compose)
+#
+# You can use this file to change any of the defaults supplied in docker-compose.yml
+# Copy this file to docker-compose.override.yml. Docker compose will read these changes for you.
+#
+# Example showing how you can enable composer support in this file:
+#
+# appdata:
+#   volumes:
+#     - ~/.composer:/var/www/.composer
+#
+# setup:
+#   environment:
+#     - M2SETUP_USE_ARCHIVE=false