Update README to include MongoDB

Issue gh-1901

Author: eleftherias

README.adoc

@@ -19,9 +19,9 @@ This Spring Session repository consists of the following modules:
 * Spring Session Data Redis - provides `SessionRepository` and `ReactiveSessionRepository` implementation backed by Redis and configuration support
 * Spring Session JDBC - provides `SessionRepository` implementation backed by a relational database and configuration support
 * Spring Session Hazelcast - provides `SessionRepository` implementation backed by Hazelcast and configuration support
+* Spring Session MongoDB - provides `SessionRepository` implementation backed by MongoDB and configuration support
 
-Additional Spring Session modules can be found in the https://github.com/spring-projects/spring-session-data-mongodb[spring-session-data-mongodb] repository
-and https://github.com/spring-projects/spring-session-data-geode[spring-session-data-geode] repository.
+Additional Spring Session modules can be found in the https://github.com/spring-projects/spring-session-data-geode[spring-session-data-geode] repository.
 
 == Getting Started