Initial YangTools information for install guide

This commit is work done by Shahida, committed by Mathieu and gotten to
the point that it builds by Colin Dixon.

Change-Id: I4d106b49ca36da25f847de92813080daa14f015c
Signed-off-by: Mathieu Lemay <mlemay@inocybe.com>
Signed-off-by: Colin Dixon <colin@colindixon.com>
Merge "Initial YangTools information for install guide"