swarming: update README.md
swarming: update README.md

Bug: b/229038581
Change-Id: I7e839f908b0f34b53daf3cb61cf1ef9cb58830c4
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/3597319
Auto-Submit: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Reviewed-by: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>
Commit-Queue: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py