raspberrypi.md: Booting guidelines
raspberrypi.md: Booting guidelines

Add guidelines how to prepare microSD card for
Raspberry Pi 2/3 and to boot AGL on the board.

Signed-off-by: Leon Anavi <15d13d7e2c6115f28df053122512bfcb5eb2dbf7@konsulko.com>

leon-anavi/docs-agl,automotive-grade-linux/docs-agl,automotive-grade-linux/docs-agl,automotive-grade-linux/docs-agl,claneys/docs-agl,claneys/docs-agl,leon-anavi/docs-agl,leon-anavi/docs-agl,leon-anavi/docs-agl,automotive-grade-linux/docs-agl,claneys/docs-agl,claneys/docs-agl