README should explain why I'd want to use this over plain-ol' exometer

[rlipscombe]

What benefits do I get from using this over directly using exometer? What trade-offs were made (i.e. is there any downside to using this)?

[Kukunin]

I can start a little (I started using it yesterday)

• auto-registration of metrics. I just put whatever metric I want to report
• it provides a neat @timed annotation, so measuring of slow methods are as easy as one line
• it feels more natural for Elixir. I use use Elixometer and update_counter instead of calling Erlang's code