Adding hint for Attachable checkbox

Work Item: 18732

--HG--
branch : 1.x

src/Orchard.Web/Modules/Orchard.ContentTypes/Views/DefinitionTemplates/ContentPartSettings.cshtml

@@ -3,5 +3,6 @@
 <fieldset>
     @Html.EditorFor(m => m.Attachable)
     <label for="@Html.FieldIdFor(m => m.Attachable)" class="forcheckbox">@T("Attachable")</label>
+    <span class="hint">@T("Check to allow this part to be attached to other content types.")</span> 
     @Html.ValidationMessageFor(m => m.Attachable)
 </fieldset>