Add clang-format section to README.md

[luishgh]

• Explain how to use clang-format
• Explain how Bananalyzer works.
• Explain both options for development workflow:
  1. Formatting locally with clang-format
  2. Relying on Bananalyzer, in that case the code after formatting must be tested.

[alanctprado]

Also add style guide:

class members should be prefixed with m_, pretty much everything is camel-cased, except for local variables, which are snake-cased,