Deprecate torflow

When we are happy with sbws as the bandwidth scanner implementation, we should add a line to Torflow README saying something like "Deprecated by sbws (url)". We should also add that line to https://github.com/TheTorProject/bwscanner (this repo might still be useful if/when sbws get refactored to use concurrency instead of multi-threading. Maybe the git.tpo repository should be moved to attic. Assigning to sbws component since we're not tracking torflow