[gspell] readme: add link to gspell for GTK 4

[Sébastien Wilmet <swilmet src gnome org>]

commit 6cf279d8753d3825b7d8ced60181b1459026597d
Author: Sébastien Wilmet <swilmet informatique-libre be>
Date:   Sat Jul 30 13:27:31 2022 +0200

    readme: add link to gspell for GTK 4

 README.md | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/README.md b/README.md
index b60bb8e..9fb628c 100644
--- a/README.md
+++ b/README.md
@@ -20,4 +20,6 @@ More information
 
 The gspell 1.x versions target **GTK 3**.
 
+gspell for GTK 4 is available [here](https://gitlab.gnome.org/otrocodigo/gspell).
+
 [More information about gspell](docs/more-information.md).