Update getting started documentation re. godep and running locally.

# *** ERROR: *** Some files are missing the required boilerplate
# header from hooks/boilerplate.txt:
#   build/common.sh
#   build/copy-output.sh
#   build/make-binaries.sh
#   build/make-build-image.sh
#   build/make-clean.sh
#   build/make-cross.sh
#   build/make-run-image.sh
#   build/release.sh
#   build/run-images/scheduler/run.sh
#   build/run-integration.sh
#   build/run-tests.sh
#   build/shell.sh
#
# Your commit will be aborted unless you fix these.
#   COMMIT_BLOCKED_ON_BOILERPLATE