i18n: git-init "Initialized [...] repository" message

i18n: git-init "Initialized [...] repository" message

These messages could benefit from splitting up.  An earlier version of
this patch began like this:

    const char *reinit_shared   = _("Reinitialized existing shared Git repository in %s\n");
    const char *init_shared     = _("Initialized empty shared Git repository in %s\n");
    const char *reinit_noshared = _("Reinitialized existing Git repository in %s\n");
    const char *init_noshared   = _("Initialized empty Git repository in %s\n");

But in the first round of gettextization I'm aiming to keep code
changes to a minimum for ease of review.  So just add a comment
explaining to translators how the sprintf format gets used so they
can cope for now if the language's grammar allows.

Signed-off-by: Ævar Arnfjörð Bjarmason <redacted>
Signed-off-by: Jonathan Nieder <redacted>
Signed-off-by: Junio C Hamano <redacted>