README.md - add instruction to setup `config.py`

Signed-off-by: Pang Yan Han <pangyanhan@gmail.com>
setup.py: Create BIN_DIR if it does not exist

Signed-off-by: Pang Yan Han <pangyanhan@gmail.com>
setup.py: Remind user to add `BIN_DIR` to PATH

Signed-off-by: Pang Yan Han <pangyanhan@gmail.com>