Update sr label to match visual label

lms/static/coffee/src/customwmd.coffee

@@ -133,7 +133,7 @@ if Markdown?
           .append($("<div>").attr("id", "wmd-preview#{_append}").addClass("wmd-panel wmd-preview"))
       $wmdPanel = $("<div>").addClass("wmd-panel")
                  .append($("<div>").attr("id", "wmd-button-bar#{_append}"))
-                 .append($("<label>").addClass("sr").attr("for", wmdInputId).text(gettext("Post body")))
+                 .append($("<label>").addClass("sr").attr("for", wmdInputId).text(gettext("Your question or idea (required)")))
                  .append($("<textarea>").addClass("wmd-input").attr("id", wmdInputId).html(initialText))
                  .append($wmdPreviewContainer)
       $elem.append($wmdPanel)