Clarify configuration of /boot

[Jeff Johnson]

In the section on /boot, it is asserted that all files needed for booting the
system are needed there, but a footnote claims that configuration files for the
boot loader belong in /etc.

This is, I think, an artifact of the way LILO used to work, where its
configuration was written into the boot sector by a user program from the
configuration. With other boot loaders such as GRUB, the boot-time
configuration is actually read from a config file on the disk, which obviously
needs to be in /boot.

I believe this arrangement was intended, but the wording in the standard is
unclear enough that Debian felt the need to explicitly override the FHS in this
regard. We should make this distinction clear.