[gtk+/gtk-3-22] Adwaita: add a comment

[Lapo Calamandrei <lapo src gnome org>]

commit 9f402d15bca284d367198998cf83823a5d7271d5
Author: Lapo Calamandrei <calamandrei gmail com>
Date:   Tue May 9 13:31:31 2017 +0200

    Adwaita: add a comment
    
    Add a comment pointing to the related bug for the dropdown menu
    margin.

 gtk/theme/Adwaita/_common.scss |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gtk/theme/Adwaita/_common.scss b/gtk/theme/Adwaita/_common.scss
index 17ba5cb..d5b90e3 100644
--- a/gtk/theme/Adwaita/_common.scss
+++ b/gtk/theme/Adwaita/_common.scss
@@ -1917,7 +1917,7 @@ menubar,
 menu,
 .menu,
 .context-menu {
-  margin: 4px;
+  margin: 4px; // see https://bugzilla.gnome.org/show_bug.cgi?id=591258
   padding: 2px 0px;
   background-color: $menu_color;
   border: 1px solid $borders_color; // adds borders in a non composited env