Adding TexShop, the LaTeX editor for MacOsX

TexShop is a stable, simple and complete LaTeX (and friends) editor for
Mac OSX. It comes normally prebundled with mactex but also exists as an
independent package.
adding the URL with the  version of TexShop
Merge pull request #1530 from meduz/texshop

Adding TexShop, the LaTeX editor for MacOsX