write some documentation about includes
write some documentation about includes

close #462

ericboehs/slim,cheunghy/slim,mojavelinux/slim,ruijsun/slim,Nikeshsuwal/slim,ruijsun/slim,fly19890211/slim,slim-template/slim,ericboehs/slim,raxoft/slim,etdev/slim,cheunghy/slim,JuanitoFatas/slim,slim-template/slim,XueQian/slim,JuanitoFatas/slim,XueQian/slim,zakuro9715/slim,sideci-sample/sideci-sample-slim,mojavelinux/slim,slim-template/slim,fly19890211/slim,yterajima/slim,metallurgical/slim,etdev/slim,Nikeshsuwal/slim,raxoft/slim,zakuro9715/slim,metallurgical/slim