Merge pull request #288 from saulshanabrook/patch-1

Add warning for mapping local volumes

docs/yml.md

@@ -75,6 +75,8 @@ expose:
 ### volumes
 
 Mount paths as volumes, optionally specifying a path on the host machine (`HOST:CONTAINER`).
+Note: Mapping local volumes is currently unsuported on boot2docker. We
+recommend you use docker-osx if want to map local volumes.
 
 ```
 volumes: