www: update README rst formatting

Signed-off-by: Nicolas Iooss <nicolas.iooss_git@polytechnique.org>
sysadmin/nat: convert to RST and rewrite some sections

Signed-off-by: Nicolas Iooss <nicolas.iooss_git@polytechnique.org>
sysadmin/pxe-boot-server: convert to RST and improve content

Merge with this blog post:
http://philpep.org/blog/installer-une-debian-rapidement-en-pxe-avec-dnsmasq

Signed-off-by: Nicolas Iooss <nicolas.iooss_git@polytechnique.org>
sysadmin/user: convert to RST

Signed-off-by: Nicolas Iooss <nicolas.iooss_git@polytechnique.org>
sysadmin/raspberrypi: convert to RST

Signed-off-by: Nicolas Iooss <nicolas.iooss_git@polytechnique.org>
Add sound configuration (MPD, PulseAudio)

Signed-off-by: Nicolas Iooss <nicolas.iooss_git@polytechnique.org>