man: reword the list of PE sections in systemd-stub

man: reword the list of PE sections in systemd-stub

Let's put the section name at the beginning of each sentence. This way we
can avoid awkward constructs like "kernel is looked for in the .linux section".
Also, since the paragraph above says that this is a list of "PE sections", we
can just say "section". In other places, it is often useful to say "PE section"
to avoid ambiguity.

Also fix the off-by-one in the count of sections.