Add Volument to README project list. (dgraph-io#854)

https://volument.com/blog/the-pain-of-a-successful-hacker-news-launch

README.md

@@ -734,6 +734,7 @@ Below is a list of known projects that use Badger:
 * [Goblero](https://github.com/didil/goblero) - Pure Go embedded persistent job queue backed by BadgerDB
 * [Surfline](https://www.surfline.com) - Serving global wave and weather forecast data with Badger.
 * [Cete](https://github.com/mosuka/cete) - Simple and highly available distributed key-value store built on Badger. Makes it easy bringing up a cluster of Badger with Raft consensus algorithm by hashicorp/raft. 
+* [Volument](https://volument.com/) - A new take on website analytics backed by Badger.
 
 If you are using Badger in a project please send a pull request to add it to the list.