Query cities for /signup route to pass into option values

[itsahsiao]

Build query per comment below, to pass into option values of signup form on html end.

Currently hard-coded.

@app.route("/signup", methods=["GET"])
def show_signup():
    """Show signup form."""

    # query cities and pass into jinja for drop down menu and option value = city id

    return render_template("signup.html")