fix xref

docs/modules/tutorials/pages/beginner/what_s_an_ide.adoc

@@ -10,7 +10,7 @@
 _Java Beans have nothing to do with this topic or NetBeans!_
 
 *  jMonkeyEngine is a game engine written in Java. You use it by putting a JAR library on the class path, and calling its +++<abbr title="Application Programming Interface">API</abbr>+++ from your Java code.
-*  The jMonkeyEngine xref:sdk.adoc[SDK] (Software Development Kit) is a customized NetBeans IDE that has special tools that help you develop 3D Java games.
+*  The jMonkeyEngine xref:sdk:sdk.adoc[SDK] (Software Development Kit) is a customized NetBeans IDE that has special tools that help you develop 3D Java games.
 
 
 [IMPORTANT]