Add p6spy, datasource-proxy and flexy-pool starters reference

Closes gh-9828

spring-boot-starters/README.adoc

@@ -49,6 +49,9 @@ do as they were designed before this was clarified.
 | http://www.couchbase.com/[Couchbase] HTTP session
 | https://github.com/mkopylec/session-couchbase-spring-boot-starter
 
+| DataSource decorating (https://github.com/p6spy/p6spy[P6Spy], https://github.com/ttddyy/datasource-proxy[datasource-proxy], https://github.com/vladmihalcea/flexy-pool[FlexyPool])
+| https://github.com/gavlyukovskiy/spring-boot-data-source-decorator
+
 | http://ff4j.org/[Feature Flipping For Java (FF4J)]
 | https://github.com/clun/ff4j/