Update nav.adoc

Author: neph1

docs/modules/sdk/nav.adoc

@@ -43,6 +43,7 @@
 ***  xref:core:scene/control/custom_controls.adoc[Custom Controls]
 ***  xref:vehicle_creator.adoc[Vehicle Creator]
 ***  xref:assetbrowser.adoc[Asset Browser]
+***  xref:animations.adoc[Animations]
 ** Advanced Usage
 ***  xref:build_platform.adoc[Building jMonkeyEngine SDK]
 ***  xref:use_own_jme#.adoc[Using your own (modified) version of jME3 in jMonkeyEngine SDK]