add legacy library usage indicator (#237)

* add legacy library usage indicator

* remove android:required

* copy line from documentation

Author: e7mac

AndroidSDKCore/src/main/AndroidManifest.xml

@@ -5,4 +5,7 @@
     <!-- Minimum permissions needed for SDK to work. -->
     <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
     <uses-permission android:name="android.permission.INTERNET"/>
+    <application>
+        <uses-library android:name="org.apache.http.legacy" android:required="false"/>
+    </application>
 </manifest>