- complete the instructions to get into USB bootloader mode
- put hardware info to the top, and split into sections
- add info about the new defconfig
- remove build size hints, which have been applied to the defconfig
- transform literal blocks into code blocks

Signed-off-by: Roland Hieber <rohieb@rohieb.name>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>