mention shortcut in the tooltip on the submit button

app/assets/javascripts/discourse/templates/composer.js.handlebars

@@ -82,7 +82,7 @@
 
         {{#if currentUser}}
           <div class='submit-panel'>
-            <button {{action save}} tabindex="4" {{bind-attr class=":btn :btn-primary :create model.cantSubmitPost:disabled"}}>{{model.saveText}}</button>
+            <button {{action save}} tabindex="4" {{bind-attr class=":btn :btn-primary :create model.cantSubmitPost:disabled"}} title="{{i18n composer.title}}">{{model.saveText}}</button>
             <a href='#' {{action cancel}} class='cancel' tabindex="4">{{i18n cancel}}</a>
           </div>
         {{/if}}

config/locales/client.en.yml

@@ -524,6 +524,7 @@ en:
       cancel: "Cancel"
       create_topic: "Create Topic"
       create_pm: "Create Private Message"
+      title: "Or press Ctrl+Enter"
 
       users_placeholder: "Add a user"
       title_placeholder: "Type your title here. What is this discussion about in one brief sentence?"