docs: fix invalid footnote syntax

docs: fix invalid footnote syntax

All footnotes must come after a separator in reStructuredText.  Fix the
two files in which this does not happen.

This mistake causes the link to be rendered literally:

   ...from the venv itself[#distlib]_. If no...

and is caught by Sphinx 8.1.0 as an unreferenced footnote.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>