[gspell] docs: hacking: refer to the docs/ dir

[Sébastien Wilmet <swilmet src gnome org>]

commit eb4a24f880cc0fafb170345e497f7f4332e74da7
Author: Sébastien Wilmet <swilmet informatique-libre be>
Date:   Sat Apr 16 18:58:52 2022 +0200

    docs: hacking: refer to the docs/ dir
    
    There is still something missing: the code conventions (they are the
    same as the gedit ones).

 HACKING | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/HACKING b/HACKING
index ccf1032..305c050 100644
--- a/HACKING
+++ b/HACKING
@@ -1,2 +1,4 @@
 gspell development
 ==================
+
+See the `docs/` directory.