ALLEN PARK, Mich. — After just eight months in Detroit, Jahmyr Gibbs is still in the infancy of his NFL career. But with each week, it seems, the Lions’ rookie running back learns something he didn’t know about the league and his place in it. His team’s place, too, for that matter. “Yeah. I was talking to somebody earlier and they said fans used to come to games with bags on their heads?” he said Wednesday, his face an odd mix of amusement and disbelief. “I guess the stadium was kinda empty then. But now, it’s electric. The whole fanbase is behind us. And it looks good to me.” As it should, wi…