[S] Change in coreboot[master]: contributing/coding_style.md: Add and clarify includes rules

[Elyes Haouas (Code Review)]

Elyes Haouas has uploaded this change for review. ( https://review.coreboot.org/c/coreboot/+/71612 )

Change subject: contributing/coding_style.md: Add and clarify includes rules
......................................................................

contributing/coding_style.md: Add and clarify includes rules

Change-Id: I3af2c3b15dda7e8b095767084dae8ee24d478256
Signed-off-by: Elyes Haouas 
---
M Documentation/contributing/coding_style.md
1 file changed, 33 insertions(+), 3 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/12/71612/1

diff --git a/Documentation/contributing/coding_style.md b/Documentation/contributing/coding_style.md
index 5b2919e3..e1199d8 100644
--- a/Documentation/contributing/coding_style.md
+++ b/Documentation/contributing/coding_style.md
@@ -921,9 +921,29 @@
 "file.h"`. Local "file.h" includes should always come separately after all
 <file.h> includes.  Headers that can be included from both assembly files and
 .c files should keep all C code wrapped in `#ifndef __ASSEMBLER__` blocks,
-including includes to other headers that don't follow that provision. Where a
-specific include order is required for technical reasons, it should be clearly
-documented with comments.
+including includes to other headers that don't follow that provision.
+The includes should be ordered alphabetically. Where a specific include order is
+required for technical reasons, it should be clearly documented with comments.
+Don't use UNIX directory '.' or '..' shortcuts and put conditional includes
+after the other includes.
+
+Example:
+```c
+#include <related_headers.h>
+#ifdef CONDITION
+#include <conditional_headers.h>
+#endif
+One blank line
+#include "local_headers.h"
+#ifdef LOCAL_CONDITION
+#include "local_conditional_headers.h"
+#endif
+One blank line
+#include <vendorcode/headers.h>
+#ifdef VENDOR_CONDITION
+#include <vendor_conditional_headers.h>
+#endif
+```

Files should generally include every header they need a definition from
 directly (and not include any unnecessary extra headers). Excepted from