Add Android readme and sample app

sharing/android/example/.gitignore

@@ -0,0 +1,16 @@
+*.iml
+.gradle
+.idea
+/local.properties
+/.idea/caches
+/.idea/libraries
+/.idea/modules.xml
+/.idea/workspace.xml
+/.idea/navEditor.xml
+/.idea/assetWizardSettings.xml
+.DS_Store
+/build
+/captures
+.externalNativeBuild
+.cxx
+local.properties