[amtk] docs: hacking: update, simplify

[Sébastien Wilmet <swilmet src gnome org>]

commit 6ce3a45efba3aaf61d62aeecd154a5f8caaf4e26
Author: Sébastien Wilmet <swilmet informatique-libre be>
Date:   Fri Apr 15 11:53:00 2022 +0200

    docs: hacking: update, simplify

 HACKING | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)
---
diff --git a/HACKING b/HACKING
index 4e6a0bf..d3dbb5c 100644
--- a/HACKING
+++ b/HACKING
@@ -1,12 +1,4 @@
-How to contribute to Amtk
-=========================
+Amtk development
+================
 
-Amtk follows the same guidelines and code conventions as GtkSourceView:
-
-    https://gitlab.gnome.org/GNOME/gtksourceview/blob/master/HACKING
-
-The Amtk GitLab:
-
-    https://gitlab.gnome.org/GNOME/amtk
-
-See also the amtk/NOTES file.
+There are some notes in the [amtk/NOTES](amtk/NOTES) file.