DOC: added and enhance documentation

CHANGELOG.md

INSTALL.md

src/doc/README_SETUP.md

src/doc/cfood.rst

src/doc/concepts.rst

src/doc/getting_started/INSTALL.md

src/doc/getting_started/helloworld.rst

src/doc/getting_started/index.rst

src/doc/getting_started/prerequisites.rst

src/doc/index.rst

src/doc/macros.rst

src/doc/tutorials/index.rst

unittests/test_converters.py