Add a readme for the Prometheus exporter. (#91)
Add a readme for the Prometheus exporter. (#91)

* Add a readme for the Prometheus exporter.

* Update README.md

nit

* Update README.md

OpenCapitals

* Clarify registration order.

census-instrumentation/opencensus-cpp,census-instrumentation/opencensus-cpp,census-instrumentation/opencensus-cpp,census-instrumentation/opencensus-cpp