[gnome-tweaks] README: sound-theme-freedesktop is required

[Jeremy Bicha <jbicha src gnome org>]

commit 7d89ca568ffada364379b97670bf2d430afdec6a
Author: Jeremy Bicha <jbicha ubuntu com>
Date:   Thu Sep 27 15:40:18 2018 -0400

    README: sound-theme-freedesktop is required
    
    Closes: https://gitlab.gnome.org/GNOME/gnome-tweaks/issues/170

 README.md | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/README.md b/README.md
index e3cd020..99e75f5 100644
--- a/README.md
+++ b/README.md
@@ -15,6 +15,7 @@ RUNTIME DEPENDENCIES
 * Python3
 * pygobject (>= 3.10)
 * gnome-settings-daemon
+* sound-theme-freedesktop
 
 * GIR files and libraries from:
   - GLib (>= 2.58)