Merge pull request moby#1674 from jbbarth/docs

Add mercurial to the list of packages needed in a dev environment

Author: metaliveblog

README.md

@@ -306,7 +306,7 @@ Setting up a dev environment
 Instructions that have been verified to work on Ubuntu 12.10,
 
 ```bash
-sudo apt-get -y install lxc curl xz-utils golang git
+sudo apt-get -y install lxc curl xz-utils golang git mercurial
 
 export GOPATH=~/go/
 export PATH=$GOPATH/bin:$PATH