Update readme (open-telemetry#421)

* chore: update README

* chore: update README

* fix: review comments

Author: mayurkale22

README.md

@@ -53,22 +53,29 @@ We have a weekly SIG meeting! See the [community page](https://github.com/open-t
 | Package                 | Description |
 | ----------------------- | -----------------|
 | [@opentelemetry/tracing](https://github.com/open-telemetry/opentelemetry-js/tree/master/packages/opentelemetry-tracing) | This module provides a full control over instrumentation and span creation. It doesn't load [`async_hooks`](https://nodejs.org/api/async_hooks.html) or any instrumentation plugin by default. It is intended for use both on the server and in the browser. |
+| [@opentelemetry/metrics](https://github.com/open-telemetry/opentelemetry-js/tree/master/packages/opentelemetry-metrics) | This module provides instruments and meters for reporting of time series data. |
 | [@opentelemetry/node](https://github.com/open-telemetry/opentelemetry-js/tree/master/packages/opentelemetry-node) | This module provides automatic tracing for Node.js applications. It is intended for use on the server only. |
+| [@opentelemetry/web](https://github.com/open-telemetry/opentelemetry-js/tree/master/packages/opentelemetry-web) | This module provides automated instrumentation and tracing for Web applications. It is intended for use in the browser only. |
 
 ### Exporters
 
 OpenTelemetry is vendor-agnostic and can upload data to any backend with various exporter implementations. Even though, OpenTelemetry provides support for many backends, vendors/users can also implement their own exporters for proprietary and unofficially supported backends. Currently, OpenTelemetry supports:
 
+#### Trace Exporters
 - [@opentelemetry/exporter-jaeger](https://github.com/open-telemetry/opentelemetry-js/tree/master/packages/opentelemetry-exporter-jaeger)
 - [@opentelemetry/exporter-zipkin](https://github.com/open-telemetry/opentelemetry-js/tree/master/packages/opentelemetry-exporter-zipkin)
 
+#### Metric Exporters
+- [@opentelemetry/exporter-prometheus](https://github.com/open-telemetry/opentelemetry-js/tree/master/packages/opentelemetry-exporter-prometheus) - WIP
+
 ### Plugins
 
 OpenTelemetry can collect tracing data automatically using plugins. Vendors/Users can also create and use their own. Currently, OpenTelemetry supports automatic tracing for:
 
 - [@opentelemetry/plugin-http](https://github.com/open-telemetry/opentelemetry-js/tree/master/packages/opentelemetry-plugin-http)
 - [@opentelemetry/plugin-grpc](https://github.com/open-telemetry/opentelemetry-js/tree/master/packages/opentelemetry-plugin-grpc)
 - [@opentelemetry/plugin-https](https://github.com/open-telemetry/opentelemetry-js/tree/master/packages/opentelemetry-plugin-https)
+- [@opentelemetry/plugin-postgres](https://github.com/open-telemetry/opentelemetry-js/tree/master/packages/opentelemetry-plugin-postgres) - WIP
 
 To request automatic tracing support for a module not on this list, please [file an issue](https://github.com/open-telemetry/opentelemetry-js/issues). Alternatively, you can [write a plugin yourself](https://github.com/open-telemetry/opentelemetry-js/blob/master/doc/plugin-guide.md).