Revert "Removed outdated metrics section"

This reverts commit 35700ff.

README.md

@@ -59,3 +59,10 @@ Send us PRs, we would love to see what you do! You can also check our GH issues
 ### Join Us
 
 WE'RE HIRING! Love Docker, Go and distributed systems? Learn more about [our open positions](https://jobs.lever.co/pachyderm/) or email us at jobs@pachyderm.io.
+
+## Usage Metrics
+
+Pachyderm automatically reports anonymized usage metrics. These metrics help us
+understand how people are using Pachyderm and make it better.  They can be
+disabled by setting the env variable `METRICS` to `false` in the pachd
+container.