Correct typo in launch documentation.

* launch/README: Fix a minor error in the path to a shell fragment
in one of the example commands.

Change-Id: Ie42e6d6b86b9518893c6661251deeab7bbce0d11
Reviewed-on: https://review.openstack.org/20429
Reviewed-by: Elizabeth Krumbach <lyz@princessleia.com>
Approved: James E. Blair <corvus@inaugust.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins