ardupilot/docs
..
config
README
build-apmrover2.sh
build-arducopter.sh
build-arduplane.sh
build-ardusub.sh
build-libs.sh
setup.sh

README

You need doxygen and graphviz installed.

Run the build-libs script first, then the project you're interested in. 
HTMl will be generated and placed into docs/projectname.