update HACK.TXT with coding style

HACK.TXT

@@ -1,5 +1,7 @@
-Capstone source is organized as followings.
+Code structure
+--------------
 
+Capstone source is organized as followings.
 
 .                   <- core engine + README + COMPILE.TXT etc
 ├── arch            <- code handling disasm engine for each arch
@@ -51,43 +53,50 @@ See bindings/<language>/README for detail instructions on how to compile &
 install the bindings.
 
 
-Adding an architecture :
+Coding style
+------------
+- C code follows Linux kernel coding style, using tabs for indentation.
+- Python code uses 4 spaces for indentation.
+
+
+Adding an architecture
+----------------------
 
 Obviously, you first need to write all the logic and put it in a new directory arch/newarch
 Then, you have to modify other files.
 (You can look for one architecture such as EVM in these files to get what you need to do)
 
-Integrate :
+Integrate:
 - cs.c
 - cstool/cstool.c
-- cstool/cstool_newarch.c : print the architecture specific details
+- cstool/cstool_newarch.c: print the architecture specific details
 - include/capstone/capstone.h
-- include/capstone/newarch.h : create this file to export all specifics about the new architecture
+- include/capstone/newarch.h: create this file to export all specifics about the new architecture
 
-Compile :
+Compile:
 - CMakeLists.txt
 - Makefile
 - config.mk
 
-Tests :
+Tests:
 - tests/Makefile
 - tests/test_basic.c
 - tests/test_detail.c
 - tests/test_iter.c
 - tests/test_newarch.c
-- suite/fuzz/fuzz_disasm.c : add the architecture and its modes to the list of fuzzed platforms
+- suite/fuzz/fuzz_disasm.c: add the architecture and its modes to the list of fuzzed platforms
 
-Bindings :
+Bindings:
 - bindings/Makefile
-- bindings/const_generator.py : add the header file and the architecture
+- bindings/const_generator.py: add the header file and the architecture
 - bindings/python/Makefile
 - bindings/python/capstone/__init__.py
-- bindings/python/capstone/newarch.py : define the python structures
-- bindings/python/capstone/newarch_const.py : generate this file
-- bindings/python/test_newarch.py : create a basic decoding test
+- bindings/python/capstone/newarch.py: define the python structures
+- bindings/python/capstone/newarch_const.py: generate this file
+- bindings/python/test_newarch.py: create a basic decoding test
 - bindings/python/test_all.py
 
-Docs :
+Docs:
 - README.md
 - HACK.txt
-- CREDITS.txt : add your name
+- CREDITS.txt: add your name