[chrome-gnome-shell] readme: update requirements

[Yuri Konotopov <ykonotopov src gnome org>]

commit 91c5a8da5ded5494044e03896c9fafef02dec7f4
Author: Yuri Konotopov <ykonotopov gmail com>
Date:   Sat Aug 6 20:09:07 2016 +0300

    readme: update requirements

 README.md |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/README.md b/README.md
index 8c6b6a9..da56d86 100644
--- a/README.md
+++ b/README.md
@@ -10,8 +10,9 @@ extensions repository https://extensions.gnome.org/, codenamed SweetTooth.
 
 Requirements
 ------------
- * GNOME Shell up to 3.18
+ * GNOME Shell up to 3.20
  * Python 2.7+
+ * PyGObject
 
 Installation
 ------------