Documentation: minor grammatical fixes and rewording in git-bundle.txt

Documentation: minor grammatical fixes and rewording in git-bundle.txt

This commit also converts all reference specifications to a monospaced font,
as the embedded ~ character used in some of the references sometimes causes
the text up to the next ~ to be displayed incorrectly as a subscript when the
HTML pages are generated. This was tested with asciidoc 8.2.5.

Signed-off-by: David J. Mellor <dmellor@whistlingcat.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>