RhIO now uses deps, which is a lightweight package manager used to handle dependencies.
First, you should install deps, then type:
deps install rhoban/rhio
RhIO and its dependencies will be downloaded and installed.
There is an example in the Skeleton directory, you can build it to try RhIO:
cd deps/packages/rhoban_rhio/Skeleton/
mkdir build
cd build
cmake ..
make
And then run the skeleton:
./skeleton
And run RhIO in another shell:
rhio
Have a look to the source of skeleton to understand how it works.