add doc/faq.txt

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>
generate ktap tutorial documentation by pandoc

add "docs" target into Makefile, then use command
"make docs" will generate tutorial.html in doc/

That tutorial.html will be www.ktap.org/doc/tutorial.html

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>