fix xref

docs/modules/sdk/pages/what_s_an_ide.adoc

@@ -93,4 +93,4 @@ image::jmonkeyplatform-docu-1.png[jmonkeyplatform-docu-1.png,width="",height="",
 You see how such a unique IDE can speed up your development process drastically, it's worth giving it a try!
 
 *  link:http://www.youtube.com/watch?v=cTErYjsJ_Yk[Video: jMonkeyEngine3 - Intro]
-*  xref:comic.adoc[jMonkeyEngine SDK - the Comic]
+*  xref:sdk:comic.adoc[jMonkeyEngine SDK - the Comic]