Unclear documentation/headers for linux

[agribov]

The libuavcan README.md file says that in order to use the library as a submodule on linux to "Please refer to the example applications supplied with the Linux platform driver for more information."

However, DroneCan repo's do not seem to host or link to these Linux drivers. OpenCyphal seems to have an archived repository containing these drivers and instructions, however that README points the user to a newer repository which has a tagged branch containing the drivers, but those appear to be deprecated based on naming, while the main branch has no drivers for linux. The archived version of the headers is the only one that contains instructions on how to set it up, and the only place that actually contains the correct CMake setup instructions for all of libuavcan.

I'd suggest having DroneCan documentation point to the correct version of the Linux drivers that users are expected to use.

Additionally, the libuavcan CMake setup seems to be a bit incorrect, and the documentation in the archived repo is the only place that shows you how to use it. I'll create a separate issue for the CMake issue.