“Inside” is Burnham’s attempt to balance his motivations as a performer and his mental health issues against the world’s inability to provide a live audience — and whether comedy is even appropriate in these times. — He got started alone in his room. Don’t let that fact slip away. Bo Burnham first shot to fame at 16 by uploading videos to a nascent website called YouTube, in which he performed vulgar but lyrically impressive comedic songs. Fourteen years later, after a career of tours and hour-long…