CONTRIBUTING.rst: Require adding braces for single statements

[norihiro]

Description

This PR adds a coding guideline to always have braces even for signle statements.

Motivation and Context

The coding style for Linux kernel requires no braces for a single statements.

• https://github.com/torvalds/linux/blob/ba36dd5ee6fd4643ebbf6ee6eefcecf0b07e35c7/Documentation/process/coding-style.rst?plain=1#L197-L211

However, the preference of this project is having braces even if the statement is single. I saw review comments like below several times.

• frontend: Change clip level to 0.0 dB #11230 (review)

How Has This Been Tested?

Check how it's rendered.

• https://github.com/norihiro/obs-studio/blob/contrib-braces-for-single-statements/CONTRIBUTING.rst#coding-guidelines

Types of changes

• Documentation (a change to documentation pages)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[Penwy]

If that is to become a required guideline, then I think it would be worth also adding a commit to add braces around all the currently unbraced single statements in the code (as far as I can see, clang-tidy can automate that).

[Fenrirthviti]

There is an internal draft of a significantly updated contribution guidelines that will be submitted in the next few weeks. We're aware of the pain points that current guidelines are a bit lacking.

As we have a working draft, I will close this, but thank you for the submission!