Manchester City finished runners-up in the Women's League Cup this season [Getty Images]Manchester City have joined Manchester United in signing up for the inaugural Women's World Sevens tournament in May.The seven-a-side competition runs between 21-23 May - three days before the Women's Champions League final - in Estoril, Portugal with a prize money pool of $5m (£3.76m).Manchester United confirmed their involvement last month with manager Marc Skinner hailing it as an "exciting opportuni