On top of more documentation I'd split the included demo from the actual SDK. User should be able to put a shared SDK in some separate folder and have their own demo projects refer to it, maybe by including a provided makefile and setting some variables to customise things. This also makes it clear where the separation between the SDK and user project is. Someone looking at this repo for the first time would have to spend time figuring that part out themselves.
I'd also make a simpler hello-world type demo project too, something really basic that's meant to show ease of use. The user can mess around with it and build upon it to get an idea of how things work. The current main.c demo in there is a bit much to be the only one included and might discourage new people from trying it. Any other changes that would help newcomers jump in without any prior knowledge would also help.