docs: Update contributor workflow
docs: Update contributor workflow

Mention that changes should be sent to GWSQ for review (to ensure
they're brought to someone's attention when ready).

Also tidy up this section somewhat.

Change-Id: I7dc810aa8fbbda9fae53cc07bdfef5789b0545c6
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/94140
Commit-Queue: Ted Pudlik <c7372cc3e451acc046049fca9e050bcb2a4a3d11@google.com>
Reviewed-by: Chad Norvell <f2b1b54074a2cea3f685a7cf4fc055999c2f0cd6@google.com>

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed