Update README.md (mongodb#2934)

Updated README.md to include mention of semantic versioning for our releases.

Author: rishitb-mongodb

README.md

@@ -121,11 +121,13 @@ their applications.
 Please refer to [spec/README.md](https://github.com/mongodb/mongo-ruby-driver/blob/master/spec/README.md) for instructions on how
 to run the driver's test suite.
 
-## Release History
+## Releases 
 
 Full release notes and release history are available [on the GitHub releases
 page](https://github.com/mongodb/mongo-ruby-driver/releases).
 
+The MongoDB Ruby driver follows [semantic versioning](https://semver.org/) for its releases.
+
 ## License
 
 Copyright (C) 2009-2020 MongoDB, Inc.