Update README with deprecation notice.

README.md

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 Telemetry Tools
 ================
 
+**This repository is deprecated.** Details on the current server for Firefox Telemetry can be found [here](https://docs.telemetry.mozilla.org/concepts/pipeline/data_pipeline.html). The current tooling for working with data can be found in the [python_moztelemetry](https://github.com/mozilla/python_moztelemetry) repo.
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 Utility code to work with Mozilla Telemetry data.
 
 Talk to us on `irc.mozilla.org` in the `#telemetry` channel, or visit the