Add help button to caldav account activity

app/src/main/java/org/tasks/caldav/CaldavAccountSettingsActivity.java

@@ -4,6 +4,7 @@ import static android.text.TextUtils.isEmpty;
 
 import android.app.ProgressDialog;
 import android.content.Context;
+import android.content.Intent;
 import android.net.Uri;
 import android.os.Bundle;
 import android.support.design.widget.Snackbar;
@@ -408,6 +409,9 @@ public class CaldavAccountSettingsActivity extends ThemedInjectingAppCompatActiv
   @Override
   public boolean onMenuItemClick(MenuItem item) {
     switch (item.getItemId()) {
+      case R.id.help:
+        startActivity(new Intent(Intent.ACTION_VIEW, Uri.parse("http://tasks.org/caldav")));
+        break;
       case R.id.remove:
         removeAccount();
         break;

app/src/main/res/menu/menu_caldav_account_settings.xml

@@ -2,6 +2,12 @@
 <menu xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:app="http://schemas.android.com/apk/res-auto">
 
+  <item
+    android:id="@+id/help"
+    android:icon="@drawable/ic_help_24dp"
+    android:title="@string/help"
+    app:showAsAction="ifRoom"/>
+
   <item
     android:id="@+id/remove"
     android:icon="@drawable/ic_delete_24dp"