Add Doxygen for the pico_binary_info macros

[lurch]

Currently we have Doxygen documentation for the pico_binary_info structs (e.g. see https://www.raspberrypi.com/documentation/pico-sdk/runtime.html#group_pico_binary_info ), but at raspberrypi/picotool#342 (comment) @will-v-pi says that it'd be more useful to document the macros, rather than documenting the structs.

[will-v-pi]

This should probably be a pico-sdk issue, as that is where the macros/structs are defined

[lurch]

This should probably be a pico-sdk issue, as that is where the macros/structs are defined

Doh!! That's obviously what I meant to do (and what I thought I'd done) - I must have been tired when creating the issue 😉