Re: doc: add missing "id" attributes to extension packaging page

Hi Brar,

An observation:  The # that shows up when hovering
over section-level headings is styled as the
section-level heading is.  But the # that shows
up when hovering over varlistentrys has the default
text style.

This works for me.  It's nice to have the "section #"s
look like the section heading.  But the varlistentry's
terms are smaller than the normal font, and their
line width is less heavy than normal.  I'm not really
invested one way or the other, but I find it kind of
nice that the varlistentry's #s are easier to click
on and more noticable because they're slightly larger
than might be expected.

Regards,

Karl 
Free Software:  "You don't pay back, you pay forward."
                 -- Robert A. Heinlein