Add missing oracle client ref in README

Author: vietj

README.adoc

@@ -12,6 +12,7 @@ Supported databases
 ** link:vertx-mysql-client[Reactive MySQL Client]
 ** link:vertx-mssql-client[Reactive MSSQL Client]
 ** link:vertx-db2-client[Reactive DB2 Client]
+** link:vertx-oracle-client[Reactive Oracle Client]
 
 This project is the natural evolution of the original Reactive PostgreSQL Client and will be part of Vert.x 3.8 stack release.