Update README.md

Author: deadtrickster

README.md

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 Ecto integration for [Prometheus.ex](https://github.com/deadtrickster/prometheus.ex)
 
+ - IRC: #elixir-lang on Freenode;
+ - [Slack](https://elixir-slackin.herokuapp.com/): #prometheus channel - [Browser](https://elixir-lang.slack.com/messages/prometheus) or App(slack://elixir-lang.slack.com/messages/prometheus).
+
 ## Quickstart
 
 1. Define your instrumenter: