add option to scroll help to top

res/menu/local_help.xml

@@ -2,6 +2,9 @@
 
 <menu xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto">
 
+    <item android:title="@string/menu_scroll_to_top"
+        android:id="@+id/log_scroll_up" />
+
     <item android:title="@string/global_menu_help_learn_desktop"
         android:id="@+id/learn_more"
         app:showAsAction="never"/>

src/org/thoughtcrime/securesms/LocalHelpActivity.java

@@ -95,6 +95,9 @@ public class LocalHelpActivity extends PassphraseRequiredActionBarActivity
             case android.R.id.home:
                 finish();
                 return true;
+            case R.id.log_scroll_up:
+                webView.scrollTo(0, 0);
+                return true;
             case R.id.learn_more:
                 openOnlineUrl("https://delta.chat");
                 return true;