message: docs: add more info to README
diff: C++ L7 proxy and communication bus
  -https://lyft.github.io/envoy
  +## Documentation
  -Watch [a video overview of Envoy](https://www.youtube.com/watch?v=RVZX4CwKhGE)
  +* [Offical documentation](https://lyft.github.io/envoy).
  +* Watch [a video overview of Envoy](https://www.youtube.com/watch?v=RVZX4CwKhGE)
  ([transcript](https://www.microservices.com/talks/lyfts-envoy-monolith-service-mesh-matt-klein/))
  to find out more about the origin story and design philosophy of Envoy.
  +* [Blog](https://medium.com/@mattklein123/envoy-threading-model-a8d44b922310) about the threading model.
  +
  +## Related
  +
  +* [envoy-api](https://github.com/lyft/envoy-api): v2 API definitions.
  +* [envoy-perf](https://github.com/lyft/envoy-perf): Performance testing framework.
  +* [envoy-filter-example](https://github.com/lyft/envoy-filter-example): Example of how to add new filters
  + and link to the main repository.
  ## Contact
  