[gparted] Update HACKING file with coding style hints and tips

[Curtis Gedak <gedakc src gnome org>]

commit 7e441c8d872f56bb4f8379fa3f41bccd1244e97f
Author: Mike Fleetwood <mike fleetwood googlemail com>
Date:   Fri Mar 19 20:23:34 2021 +0000

    Update HACKING file with coding style hints and tips

 HACKING | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)
---
diff --git a/HACKING b/HACKING
index d7ef5b89..dbcdd49b 100644
--- a/HACKING
+++ b/HACKING
@@ -20,6 +20,22 @@ Curtis
 
 
 
+Coding style
+============
+
+The GParted code is all over the place in terms of coding style.  New
+code, and updated code where reasonable, should use Allman style and
+Smart Tabs alignment.  See src/OptionComboBox.cc and
+src/SupportedFileSystems.cc as examples.  Don't worry too much about the
+style, we can always adjust it if necessary during the review and merge
+process.
+
+* https://en.wikipedia.org/wiki/Indentation_style#Allman_style
+* https://www.emacswiki.org/emacs/SmartTabs
+* https://vim.fandom.com/wiki/Indent_with_tabs,_align_with_spaces
+
+
+
 Translatable files
 ==================