Update style guidance in HACKING file

HACKING

@@ -84,18 +84,13 @@ patches if you can.
 Style
 -----
 
-When contributing new code, we suggest using two-space indents with no
+Code style guidelines and quality checking tools are documented at
-tabs.  This is generally the default in emacs, and Vim users can
+https://secwiki.org/w/Nmap/Code_Standards . The short version is:
-achieve it by adding rules such as the following to .vimrc:
-
-if getcwd() =~ '/nmap'
-    set nocindent
-    set expandtab
-    set softtabstop=2
-    set shiftwidth=2
-    set copyindent
-endif
 
+* Indent with 2 spaces, not tabs
+* No trailing whitespace
+* Be consistent
+* Use comments
 
 Credits
 -------