[mutter] README: Mention usage by Gala

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 4a7a803c340acca9f32641bee1b925eab7519a05
Author: Peter Uithoven <peter peteruithoven nl>
Date:   Thu Nov 8 15:03:35 2018 +0000

    README: Mention usage by Gala

 README.md | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)
---
diff --git a/README.md b/README.md
index 77a8ad953..56141d1a2 100644
--- a/README.md
+++ b/README.md
@@ -17,9 +17,10 @@ Internally it uses a fork of Cogl, a hardware acceleration abstraction library
 used to simplify usage of OpenGL pipelines, as well as a fork af Clutter, a
 scene graph and user interface toolkit.
 
-Mutter is used by GNOME Shell, the GNOME core user interface. It can also be run
-standalone, using the command "mutter", but just running plain mutter is only
-intended for debugging purposes.
+Mutter is used by, for example, GNOME Shell, the GNOME core user interface, and
+by  Gala, elementary OS's window manager. It can also be run standalone, using
+the  command "mutter", but just running plain mutter is only intended for
+debugging purposes.
 
 ## License