(Reuters) - British food delivery firm Deliveroo said on Thursday founder and CEO Will Shu will step down once its takeover by U.S. rival DoorDash takes effect. U.S. meal delivery firm DoorDash in May agreed to buy Deliveroo in a deal valuing the British rival at about 2.9 billion pounds ($3.96 billion), banking on their combined reach and local expertise to take on competition. "I have decided that now is the right time for me to step down," said Shu, who founded Deliveroo in 2013, alongside his childho ...