development.md: show override PROJECT_ID (#3369)
development.md: show override PROJECT_ID (#3369)

I assume most people are not on the knative-environments project.
So showing how to override the default in the build/deploy doc.

Signed-off-by: Ahmet Alp Balkan <c786c8527fd6be7431bb94ca48b6f76cc06787cc@google.com>
knative/serving,knative/serving