Add shortcut help for 'toggle play queue'

libresonic-main/src/main/resources/org/libresonic/player/i18n/ResourceBundle_en.properties

@@ -267,6 +267,7 @@ more.keyboard.more = Go to More
 more.keyboard.about = Go to About
 more.keyboard.search = Search
 more.keyboard.sidebar = Toggle left sidebar
+more.keyboard.playqueue = Toggle play queue
 more.keyboard.shortcuts = Show keyboard shortcuts
 more.keyboard.then = then
 more.mobile.title = Mobile phone