Merge pull request #1704 from dhrp/ubuntu-install-finger-fingerprint

added apt-key finger tip and fingerprint in ubuntu installation page

docs/sources/installation/ubuntulinux.rst

@@ -74,6 +74,7 @@ Docker is available as a Debian package, which makes installation easy.
 .. code-block:: bash
 
    # Add the Docker repository key to your local keychain
+   # using apt-key finger you can check the fingerprint matches 36A1 D786 9245 C895 0F96 6E92 D857 6A8B A88D 21E9
    sudo sh -c "curl https://get.docker.io/gpg | apt-key add -"
 
    # Add the Docker repository to your apt sources list.
@@ -127,6 +128,7 @@ to follow them again.*
 .. code-block:: bash
 
    # Add the Docker repository key to your local keychain
+   # using apt-key finger you can check the fingerprint matches 36A1 D786 9245 C895 0F96 6E92 D857 6A8B A88D 21E9
    sudo sh -c "curl http://get.docker.io/gpg | apt-key add -"
 
    # Add the Docker repository to your apt sources list.