Add DEPENDS to bash/release.sh, and update DESIGN.md to reflect
how dependencies are handled.

BUG=skia:

Review URL: https://codereview.chromium.org/824743002
This allows to poll for the current status of HEAD with measures of how many items are untriaged or negative (in HEAD).

BUG=skia:2930

Review URL: https://codereview.chromium.org/818093002