Update Lesson2.md to include information about updating a commit after it has been pushed to the remote repository. Change-Id: Iebf86113b13d859d9c9e3db51e22ea44cb1144f6 Signed-off-by: Evelyn Huang <evhuang@google.com> Reviewed-on: https://review.coreboot.org/20948 Tested-by: build bot (Jenkins) <no-reply@coreboot.org> Reviewed-by: Martin Roth <martinroth@google.com>