add bash notes on special parameters + future ref
add bash notes on special parameters + future ref

erictleung/programming-notes,erictleung/programming-notes,erictleung/programming-notes,erictleung/programming-notes,erictleung/programming-notes,erictleung/programming-notes,erictleung/programming-notes,erictleung/programming-notes,erictleung/programming-notes