Add example command for how to find SHA1 of an external ID
Add example command for how to find SHA1 of an external ID

Change-Id: Iab96ab10c65cd3b1935cd5ff6f4fa671b89b3095
(cherry picked from commit 7bc254269476269ec020cb10d72829656352ee94)

GerritCodeReview/gerrit,WANdisco/gerrit,WANdisco/gerrit,qtproject/qtqa-gerrit,qtproject/qtqa-gerrit,WANdisco/gerrit,WANdisco/gerrit,WANdisco/gerrit,GerritCodeReview/gerrit,WANdisco/gerrit,qtproject/qtqa-gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,qtproject/qtqa-gerrit,qtproject/qtqa-gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,GerritCodeReview/gerrit,qtproject/qtqa-gerrit,WANdisco/gerrit,GerritCodeReview/gerrit,qtproject/qtqa-gerrit