add comment for localizers to insert their credit information

browser/base/locale/credits.html

@@ -224,7 +224,15 @@
             Boris Zbarsky<br>
           </div>
         </div>
-        
+
+<!-- LOCALIZERS: Add your translation credits here!
+        <div class="creditsGroup">
+          <h3>Translators</h3>
+          <div class="credit">
+            Translator Name<br>
+          </div>
+        </div>
+-->         
         <div class="creditsGroup">
           <h3>Visual Design Coordinator</h3>
           <div class="credit">Steven Garrity</div>