update TODO
man: don't document ".include" in configuration files anymore as first step to deprecate them one day
man: split settings documentaiton in systemd.unit(5) into two sections
man: suffix networkd config file options with "="

That's what we do for all options in the other man pages. It helps
clarifying that these are options that values need to be assigned to.
update TODO
install: networkd.service depend on !--disable

It doesn't make any sense to symlink this unit file into /etc when the
unit file itself isn't even installed, with --disable-networkd. This
moves the GENERAL_ALIASES logic into the right "if" block.