Add content description to plus string

Bug: 14588275
Change-Id: Ia4be542c609934def61232bb15babd5dad4179bf
diff --git a/res-common/values/strings.xml b/res-common/values/strings.xml
index 0346d4e..3f195ad 100644
--- a/res-common/values/strings.xml
+++ b/res-common/values/strings.xml
@@ -736,6 +736,7 @@
     -->
     <string name="description_delete_button">backspace</string>
 
+    <!--  String describing the button used to add a plus (+) symbol to the dialpad -->
     <string name="description_image_button_plus">plus</string>
 
     <!-- String describing the Voicemail ImageButton