Add syntax highlighting in "README.md"

[zhoukaidev]

Before highlighting

// Equivalent to enum class MoreColor : int64_t {BLUE, BLACK = 1};
WISE_ENUM_CLASS((MoreColor, int64_t), BLUE, (BLACK, 1))

// Inside a class, must use a different macro, but still works
struct Bar {
    WISE_ENUM_MEMBER(Foo, BUZ)
};

// Adapt an existing enum you don't control so it works with generic code
namespace another_lib {
enum class SomebodyElse { FIRST, SECOND };
}
WISE_ENUM_ADAPT(another_lib::SomebodyElse, FIRST, SECOND)

After highlighting

// Equivalent to enum class MoreColor : int64_t {BLUE, BLACK = 1};
WISE_ENUM_CLASS((MoreColor, int64_t), BLUE, (BLACK, 1))

// Inside a class, must use a different macro, but still works
struct Bar {
    WISE_ENUM_MEMBER(Foo, BUZ)
};

// Adapt an existing enum you don't control so it works with generic code
namespace another_lib {
enum class SomebodyElse { FIRST, SECOND };
}
WISE_ENUM_ADAPT(another_lib::SomebodyElse, FIRST, SECOND)

[quicknir]

Cheers, thanks!