Added eXist-db , XML-based Database

README.md

@@ -505,6 +505,7 @@
   * [MongoDB](https://www.mongodb.org/) - Another document-oriented database system.
   * [RavenDB](http://ravendb.net/) - Document based database with ACID/Transactional features.
   * [RethinkDB](http://www.rethinkdb.com/) - Distributed document store database, focuses on JSON.
+  * [eXist-DB] (Https://www.exist-db.org/) - Open Source XML Database
 * Graph
   * [FlockDB](https://github.com/twitter/flockdb) - Twitter's distributed, fault-tolerant graph database.
   * [Neo4j](http://neo4j.com/) - Graph database.