Add commit message rules in the CONTRIBUTING file (#17335)

Co-authored-by: pancake <pancake@nopcode.org>
Co-authored-by: Riccardo Schirone <ret2libc@users.noreply.github.com>
Co-authored-by: Khairul Azhar Kasmiran <kazarmy@gmail.com>
Co-authored-by: Anton Kochkov <xvilka@gmail.com>

CONTRIBUTING.md

@@ -27,6 +27,7 @@ try to keep the codebase consistent and clean.
 
   and be sure to follow the CODINGSTYLE (more on this in [DEVELOPERS.md][]).
 * Submit the Pull Request(PR) on Github.
+* Prefix the PR title with `WIP:` if it's not yet ready to be merged
 * When relevant, write a test in [test/](test).
 
 ## Rebasing onto updated master
@@ -71,6 +72,52 @@ When afraid to touch force and risk losing your work (do backups!..),
 try *merging master into your branch* instead of rebasing onto it.
 This is discouraged, as it produces ugly hard-to-maintain commit history.
 
+## Commit message rules
+
+When commiting your changes into the repository you may want to follow some
+rules to make the git history more readable and consistent:
+
+* Start the message capitalized (only the first character must be in uppercase)
+* Be short and concise, the whole concept must fit one line
+* If a command is inlined, use backticks
+* Add a double-hashtag if the change matters for the changelog (See below)
+* If the commit fixes a bug start with 'Fix #number - '
+* For extra details, add an empty line and use asterisk item list below
+* Use present simple grammar tense (Add vs Added, Fix vs Fixed/Fixes)
+
+### Commit message hashtag list:
+
+* ##anal     - analysis related
+* ##asm      - assembler
+* ##bin      - binary parsing
+* ##build    - build fixes/changes
+* ##config   - config var changes/additions/renamings
+* ##cons     - console/terminal-related
+* ##crypto   - cryptography
+* ##debug    - debugger stuff
+* ##diff     - diffing code, strings, basic blocks, ...
+* ##disasm   - disassembler
+* ##doc      - documentation
+* ##egg      - the `r_lang` compiler
+* ##emu      - emulation, including esil
+* ##graph    - basic block graph, callgraph, ...
+* ##io       - related to the `r_io` library
+* ##json     - json fixes/changes
+* ##lang     - bindings
+* ##meta     - metadata handling other than printing
+* ##optimization-space/time optimizations
+* ##port     - portability (new OS/archs)
+* ##print    - printing data, structures, strings, tables, types ..
+* ##projects - saving/loading state
+* ##refactor - improve code quality
+* ##remote   - r2 over tcp, http, rap, serial .. including collaboration
+* ##search   - rafind2, / command, ..
+* ##shell    - commandline, newshell, ..
+* ##signatures-searching/generating them
+* ##test     - testing infrastructure fixes/changes
+* ##tools    - r2pm, rarun2, rax2 ... that don't fit in other categories
+* ##util     - core apis
+* ##visual   - visual ui, including panels
 
 # Additional resources