Documentation: note styling for bit fields

Our codebase uses a lot of bit field variables, generally to mark boolean type variables. While there is a formatting rule in the '.clang-format', there is no guideline specified in the 'CodingGuidelines'. Since the '.clang-format' is not yet enforced, let's also add a guideline with the same rule as mentioned in the '.clang-format', which is to not use any spaces around the colon, like so: unsigned my_field:1; unsigned other_field:1; unsigned field_with_longer_name:1; This would allow us not to modify the clang-format file, and more importantly, discourage people from doing ugly alignment with spaces, i.e. unsigned my_field : 1; unsigned other_field : 1; unsigned field_with_longer_name : 1; Helped-by: Junio C Hamano <gitster@pobox.com> Signed-off-by: Karthik Nayak <karthik.188@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>