Volumes can be files

Just wanted to add that is possible to mount files as volumes. 

Don't know if that is worth mentioning. But it can be useful if you want to toy around with a image from [Docker Hub](https://hub.docker.com) without writing your own Dockerfile.

README.md

@@ -429,6 +429,8 @@ You can use remote NFS volumes if you're [feeling brave](https://docs.docker.com
 
 You may also consider running data-only containers as described [here](http://container42.com/2013/12/16/persistent-volumes-with-docker-container-as-volume-pattern/) to provide some data portability.
 
+[Be aware that you can mount files as volumes.](#volumes-can-be-files)
+
 ## Exposing ports
 
 Exposing incoming ports through the host container is [fiddly but doable](https://docs.docker.com/engine/reference/run/#expose-incoming-ports).
@@ -770,6 +772,21 @@ Remove all exited containers
 docker rm -f $(docker ps -a | grep Exit | awk '{ print $1 }')
 ```
 
+### Volumes can be files
+
+Be aware that you can mount files as volumes. For example you can inject a configuration file like this:
+
+``` bash
+# copy file from container
+docker run --rm httpd cat /usr/local/apache2/conf/httpd.conf > httpd.conf
+
+# edit file
+vim httpd.conf
+
+# start container with modified configuration
+docker run --rm -ti -v "$PWD/httpd.conf:/usr/local/apache2/conf/httpd.conf:ro" -p "80:80" httpd
+```
+
 ## Contributing
 
 Here's how to contribute to this cheat sheet.