Add link to the logdog RPCExplorer to README
Add link to the logdog RPCExplorer to README

Change-Id: I434f3c25c5d5772a1f3bed52723647f5e44b5606
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/1924984
Reviewed-by: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Commit-Queue: Gregory Guterman <8788ef0c8716b810f5f3059185bc1437e34caf28@google.com>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go