Is your feature request related to a problem? Please describe.
Greetings! I just started using opencensus in go. The quality and framework was super easy to use, the primitives are intuitive and there are great docs! One thing I noticed was that runtime (runmetrics) metrics didn't include GC information. I'm wondering if runmetrics are a good place to include these metrics?

Describe the solution you'd like
If runmetrics is a good place to include these metrics, I was hoping to have gc stats included in the runtime metrics exported.

Describe alternatives you've considered
I could pretty easily instrument these in my own application, even package it as a library so all my go apps could easily get these metrics.

Additional context

This request is based on the runtime metrics that prometheus go client ships with.

Can see the prometheus metrics in action on their grafana dashboard:

Thank you!!!