[gtk] Add a build status badge

[Emmanuele Bassi <ebassi src gnome org>]

commit 9165dd33ede53969ecda77473baa4eba9266c306
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Wed Mar 21 00:45:09 2018 +0000

    Add a build status badge
    
    Like all cool kids are doing, these days.

 README.md | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/README.md b/README.md
index 64aa178098..eb7a135dcc 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,8 @@
 GTK+ — The GTK toolkit
 ======================
 
+[![Build 
Status](https://gitlab.gnome.org/GNOME/gtk/badges/master/build.svg)](https://gitlab.gnome.org/GNOME/gtk/pipelines)
+
 General information
 -------------------