"This letter is to inform you that I will be resigning my position as [insert position] effective [insert last day, preferably a two-week notice]. It has been a pleasure working here and I am grateful for the opportunity."
There is no need to discuss the reason(s) why you are leaving or to say anything else but the last day you'll be there. Because when you will reach this point you will be no longer be judged for your literature skills, on the outside chance you are, it no longer matters.