Update ubuntulinux.md and debian.md

to add bash completion for the docker command

docs/sources/installation/debian.md

@@ -30,6 +30,7 @@ To install the latest Debian package (may not be the latest Docker release):
     $ sudo apt-get update
     $ sudo apt-get install docker.io
     $ sudo ln -sf /usr/bin/docker.io /usr/local/bin/docker
+    $ sudo sed -i '$acomplete -F _docker docker' /etc/bash_completion.d/docker.io
 
 To verify that everything has worked as expected:
 

docs/sources/installation/ubuntulinux.md

@@ -36,6 +36,7 @@ To install the latest Ubuntu package (may not be the latest Docker release):
     $ sudo apt-get update
     $ sudo apt-get install docker.io
     $ sudo ln -sf /usr/bin/docker.io /usr/local/bin/docker
+    $ sudo sed -i '$acomplete -F _docker docker' /etc/bash_completion.d/docker.io
 
 To verify that everything has worked as expected: