Added codeblocks for example commands

Markdown enhancements. 

Visual diff:
https://github.com/openvswitch/ovs/blob/master/vtep/README.ovs-vtep.md#startup
https://github.com/Scorpiion/ovs/blob/master/vtep/README.ovs-vtep.md#startup

Signed-off-by: Robert Åkerblom-Andersson <Robert.nr1@gmail.com>