Instruct using git cl archive -f instead of git branch -D to archive
landed and closed branches.

Bug: None
Change-Id: Id28a79d88cf80b2d3b6c70015bc26c0e173efdf3
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/8424626
Commit-Queue: Simon Zünd <szuend@chromium.org>
Reviewed-by: Simon Zünd <szuend@chromium.org>