Rivian’s stock fell 18% on Monday, but it’s hard to imagine the company’s executives are too upset. Why? Because the automaker seems to be on the verge of starting work on its long-awaited second factory, 45 miles east of downtown Atlanta.Let’s do some reading between the lines. Rivian has had a great few weeks. The EV maker announced last week that it is on track to sell about 3,000 more cars this year than expected, and its stock has been on a…