Serena Williams is back on the tour. Beginning this week, Williams will be playing doubles at the Queen’s Club Championships alongside Canadian teenager and world No. 9 Victoria Mboko . She will also play doubles at the Berlin Open later this month. Why did she choose to come back at age 44? The answer was easy. “Why not? For lack of a better explanation,” Williams said at Queen’s Club in London Sunday. Williams, who has 39 Grand Slam titles between her illustrious singles and doubles careers,