Why now might be a great time to buy Starbucks stock.According to recent reports, billionaire Paul Singer and his activist hedge fund Elliott Investment Management have taken a large position in Starbucks (SBUX -1.82%). The coffee house operator has seen its stock struggle in recent years. It's down over 15% in the past five years, while the S&P 500 is up over 85% during the same stretch.With Elliott's involvement, should investors follow suit and pile into Starbucks shares?Elliott's Starbucks stakeElliott' ...