add formatting rules to contributing guide (#190)

CONTRIBUTING.md

@@ -5,30 +5,33 @@ How to contribute
 Getting Started
 ---------------
 
--  Pick a feature from the [TODO Features](https://github.com/cieslarmichal/faker-cxx/blob/main/TODO.md) or [Issues](https://github.com/cieslarmichal/faker-cxx/issues). You could also implement your own module/functions.
--  If you picked a feature from list, please create an issue for it (so other contributors don't implement the same feature). 
--  Fork the repository on GitHub
+- Pick a feature from the [TODO Features](https://github.com/cieslarmichal/faker-cxx/blob/main/TODO.md)
+  or [Issues](https://github.com/cieslarmichal/faker-cxx/issues). You could also implement your own module/functions.
+- If you picked a feature from list, please create an issue for it (so other contributors don't implement the same
+  feature).
+- Fork the repository on GitHub
 
 Making Changes
 --------------
 
--  Create a feature/bug branch from main branch:
+- Create a feature/bug branch from main branch:
 
-   ``git checkout -b feature/feature-name``
-   
-   Please avoid working directly on the ``main`` branch.
--  Make commits of logical units.
--  Make sure you have added the necessary tests for your changes.
--  Run *all* the tests to assure nothing else was accidentally broken.
+  ``git checkout -b feature/feature-name``
+
+  Please avoid working directly on the ``main`` branch.
+- Make commits of logical units.
+- Make sure you have added the necessary tests for your changes.
+- Run *all* the tests to assure nothing else was accidentally broken.
 
 Submitting Changes
 ------------------
 
--  Push your changes to the branch in your fork of the repository.
--  Submit a pull request to the repository.
+- Format code with ``clang-format src/**/*.cpp src/**/*.h include/**/*.h -i -style=file``
+- Push your changes to the branch in your fork of the repository.
+- Submit a pull request to the repository.
 
 Additional Resources
 ====================
 
--  If you have any questions about features you can join [Discord Channel](https://discord.com/invite/h2ur8H6mK6).
--  Features implementations in [Faker.js](https://github.com/faker-js/faker) could be helpful as a reference.
+- If you have any questions about features you can join [Discord Channel](https://discord.com/invite/h2ur8H6mK6).
+- Features implementations in [Faker.js](https://github.com/faker-js/faker) could be helpful as a reference.