[addressbook] Claim what image size is expected when asking to resize given image

src/addressbook/addressbook.error.xml

@@ -87,6 +87,7 @@
 
   <error type="question" id="prompt-resize" default="GTK_RESPONSE_YES">
     <_primary>The image you have selected is large. Do you want to resize and store it?</_primary>
+    <_secondary>An expected image size is up to 96 x 96 pixels.</_secondary>
     <button _label="_Resize" response="GTK_RESPONSE_YES"/>
     <button _label="_Use as it is" response="GTK_RESPONSE_NO"/>
     <button _label="_Do not save" response="GTK_RESPONSE_CANCEL"/>