OWNERS.general: add myself

Interested in helping out with the review load.  I put myself in
g/cros-portage-reviewers already (not sure if that's needed for gwsq?)

BUG=none
TEST=presubmit

Change-Id: I7d8720e84acc9d685e7d477c915c578f120764c4
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/portage-stable/+/2490239
Tested-by: Jack Rosenthal <jrosenth@chromium.org>
Reviewed-by: Manoj Gupta <manojgupta@chromium.org>
Commit-Queue: Jack Rosenthal <jrosenth@chromium.org>