Add missing shortcut help for 'r', refresh

src/main/app/i18n/ar.js

@@ -175,7 +175,8 @@
       "font_size" : "increase/decrease font size of the current entry ",
       "go_to_all" : "go to the All view ",
       "go_to_starred" : "go to the Starred view ",
-      "feed_search" : "navigate to a subscription by entering the subscription name"
+      "feed_search" : "navigate to a subscription by entering the subscription name",
+      "refresh": "refresh"
     }
   }
-}
+}

src/main/app/i18n/en.js

@@ -177,7 +177,8 @@
       "font_size" : "increase/decrease font size of the current entry",
       "go_to_all" : "go to the All view",
       "go_to_starred" : "go to the Starred view",
-      "feed_search" : "navigate to a subscription by entering the subscription name"
+      "feed_search" : "navigate to a subscription by entering the subscription name",
+      "refresh": "refresh"
     }
   }
-}
+}

src/main/app/templates/_shortcuts.html

@@ -1,4 +1,7 @@
 <dl class="dl-horizontal">
+	<dt>r</dt>
+	<dd>{{ 'about.shortcuts.refresh' | translate }}</dd>
+
 	<dt>j</dt>
 	<dd>{{ 'about.shortcuts.open_next_entry' | translate }}</dd>
 
@@ -68,4 +71,4 @@
 	</dt>
 	<dd>{{ 'about.shortcuts.feed_search' | translate }}</dd>
 
-</dl>
+</dl>