Add update library menu item

app/src/main/res/values/strings.xml

@@ -504,6 +504,9 @@
     <string name="transition_pages_loading">Loading pages…</string>
     <string name="transition_pages_error">Failed to load pages: %1$s</string>
 
+    <!-- Updates fragment -->
+    <string name="updating_library">Updating library</string>
+
     <!-- History fragment -->
     <string name="recent_manga_source">%1$s - Ch.%2$s</string>