doc: correct prometheus exporter description in README (#121)

Author: kjin

packages/opencensus-exporter-prometheus/README.md

@@ -1,9 +1,9 @@
 # OpenCensus Prometheus Exporter for Node.js
 [![Gitter chat][gitter-image]][gitter-url]
 
-OpenCensus Prometheus Exporter allows the user to send collected traces with [OpenCensus Node.js](https://github.com/census-instrumentation/opencensus-node) to Prometheus.
+The OpenCensus Prometheus Exporter allows the user to send collected stats with [OpenCensus Node.js](https://github.com/census-instrumentation/opencensus-node) to Prometheus.
 
-This project is still at an early stage of development. It's subject to change.
+This package is still at an early stage of development, and is subject to change.
 
 ## Installation
 
@@ -48,9 +48,9 @@ tracing.registerExporter(exporter).start();
 ```
 
 ## Useful links
-- To know more about Prometheus, visit: <https://prometheus.io/>
+- To learn more about Prometheus, visit: <https://prometheus.io/>
 - For more information on OpenCensus, visit: <https://opencensus.io/>
-- To checkout the OpenCensus for Node.js, visit: <https://github.com/census-instrumentation/opencensus-node>
+- To checkout OpenCensus for Node.js, visit: <https://github.com/census-instrumentation/opencensus-node>
 - For help or feedback on this project, join us on [gitter](https://gitter.im/census-instrumentation/Lobby)
 
 [gitter-image]: https://badges.gitter.im/census-instrumentation/lobby.svg