Documentation/git-svn: improve asciidoctor compatibility

Documentation/git-svn: improve asciidoctor compatibility

The second paragraph in the CONFIGURATION section intends to emphasize
the word 'must' with bold type. It does so by writing it as *must*, and
this works fine with AsciiDoc. It usually works great with Asciidoctor,
too, but in this particular instance, we have another "*" earlier in the
paragraph. We do escape it, and it is rendered literally just like we
want it to, but Asciidoctor then ends up tripping on the second (or
third) of the asterisks in this paragraph.

Since that asterisk is (part of) a literal example, we can set it in
monospace, by giving it as `*`. Adjust the whole paragraph in this way.
There's lots more monospacing to be done in this document, but since our
main motivation is addressing AsciiDoc/Asciidoctor discrepancies like
this one, let's just convert this one paragraph.

Signed-off-by: Todd Zullinger <tmz@pobox.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>