msi: Tweak msiexec's usage message.

[Julian Rüger]

Hi Francois and wine-devel,

while we're at it, shouldn't these

>"Advertise a product:\n"
>"\t/j[u|m] package [/t transform] [/g languageid]\n"
>"Apply a patch:\n"
>"\t/p patch_package [property]\n"
>"\t/p patch_package /a package [property]\n"

also be put in curly brackets?

Like this:

\t/j[u|m] {package} [/t transform] ...
\t/p {patch_package} [property]\n
...

Best,
Julian