Add warning about changing external IDs manually
Add warning about changing external IDs manually

External IDs are stored in a notes branch where the note key is the SHA1
of the external ID key. This means if the external ID is changed the
note key must be recomputed.

Change-Id: I41fc1daaf861b4db385ead01a7bf2ab4119617bb
Signed-off-by: Edwin Kempin <d43fb6c98c97e553b671ed9a9318100f1de386e7@google.com>

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