Futher clarified bullet use.

src/docs/asciidoc/jme3/jme3_source_structure.adoc

@@ -55,10 +55,10 @@ a| Source Package
 a| Description
 
 <a| src/jbullet
-a| Game Physics Engine, based on the jBullet framework. +++<strike>Bullet</strike>+++
+a| Game Physics Engine, based on the jBullet framework. Desktop only. +++<strike>Bullet</strike>+++
 
 <a| src/bullet
-a| Game Physics Engine, based on the native Bullet framework. +++<strike>jBullet</strike>+++
+a| Game Physics Engine, based on the native Bullet framework. Needs jme3-bullet-native or jme3-bullet-native-android (beta) +++<strike>jBullet</strike>+++
 
 a| src/bullet-common
 a| Classes common between native and java Bullet implementations.