wwwtext: config comment improvements

wwwtext: config comment improvements

Use the full URL of the inbox being mirrored to reduce ambiguity
(instead of just the inbox name).

Using asymmetric quotes (e.g `foo') improves readability for me
in that it's more obvious when a quote begins and ends.  It also
lights up fewer pixels and reduces visual noise compared to
double-quotes.

We'll also reflow the `mainrepo' vs `inboxdir' comment slightly
to emphasize the word `instead'.