Documentation📄: Add MDX Docs in `Writing Documentation` section

What is the current documentation state?

The documentation explains various practices to follow for contribution to Moja global repository. But even though MDX has been used in most of the documents, there is no current explanation on MDX.

Where is this stated?

https://docs.moja.global/en/latest/contributing/code_contribution_best_practices.html#writing-documentation

Why do you want to improve the statement?

Because Most of the documents use .mdx extension, many people especially beginners are confused. So I want to remove the confusion.

Proposed Statement

I will give a proper explanation on MDX by going through various resources.

Additional context.

Please assign this issue to me since I am really interested to work with it.