Backport missing 3rd party starter reference

Author: snicoll

spring-boot-starters/README.adoc

@@ -112,6 +112,9 @@ do as they were designed before this was clarified.
 | http://infinispan.org/[Infinispan]
 | https://github.com/infinispan/infinispan-spring-boot
 
+| http://restfb.com/[RestFB] Messenger
+| https://github.com/marsbits/restfbmessenger
+
 | http://square.github.io/okhttp/[OkHttp]
 | https://github.com/freefair/okhttp-spring-boot