message: [docs] CODING_STYLE: update
diff: +
  # Coding Style Guidelines
  +- Prefer CppCoreGuidelines if possible.
  +- Avoid `friend` keyword.
  +- Use signed integers unless the integer is holding a bit pattern.
  +- Use the smallest integer type that is required to hold all desired values.
  +- Do not cast from signed to unsigned unless you want the bit pattern, prefer to cast from unsigned
  + to signed instead.
  ## Naming Conventions
  