[gnome-shell] Fix README link

[Florian Müllner <fmuellner src gnome org>]

commit 614c4480e2f0defcaab0c3226f4c4876f9fe62ab
Author: Harry Mallon <hjmallon gmail com>
Date:   Sat Sep 1 15:01:46 2018 +0100

    Fix README link

 README.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/README.md b/README.md
index 6bec164c4..137faa602 100644
--- a/README.md
+++ b/README.md
@@ -7,7 +7,7 @@ easy to use experience.
 
 For more information about GNOME Shell, including instructions on how
 to build GNOME Shell from source and how to get involved with the project,
-see the [project wiki][wiki]
+see the [project wiki][project-wiki].
 
 Bugs should be reported to the GNOME [bug tracking system][bug-tracker].