message: added section on code documentation to style guide.
diff: @@ -129,3 +129,34 @@ varying void *; // `varying` is meaningless, void has no varyingness to it
  - Minimize the number of alias names given to both object types and
  parameters.
  +## Code Documentation
  +
  +Code documentation should be in terms of C++ style single-line comments or
  +multi-line C style comments, e.g.:
  +
  +```cpp
  +// Lorem ipsum dolor sit amet
  +
  +/* Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod
  + * tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam,
  + * quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo
  + * consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse
  + * cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non
  + * proident, sunt in culpa qui officia deserunt mollit anim id est laborum. */
  +```
  +
  +Avoid Doxygen-style code documentation, such as
  +
  +```cpp
  +/*! comment style to avoid */
  +
  +//! comment style to avoid
  +
  +/*! \brief comment style to avoid */
  +
  +int var; //!< comment style to avoid
  +```
  +
  +When adding or updating public API definitions, update the corresponding API.md
  +documentation as part of your merge request. This keeps our documentation always
  +current, and minimizes the need for audits at release time.
  