git-clone.txt: Fix grammar and formatting

git-clone.txt: Fix grammar and formatting

Add the missing definite article ("the") in several places.

Change "note to..." to "note for...", since "note to" means that
that the note is addressed to someone (source: Google search).

Change "progressbar" to "progress bar" (source: Wikipedia).

Format git commands, options, and file names consistently using
back quotes (i.e. a fixed font in the resulting HTML document).

Signed-off-by: Björn Gustavsson <bgustavsson@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>