updated mac and windows install instructions

...instructions/macintosh/images/associate_with_launcher.png

installation_instructions/macintosh/images/cannot_open.png

..._instructions/macintosh/images/cannot_verify_notebook.png

installation_instructions/macintosh/images/launcher_logo.png

...llation_instructions/macintosh/images/on_first_launch.png

...ation_instructions/macintosh/images/on_open_in_finder.png

...ation_instructions/macintosh/installation_instructions.md

...llation_instructions/windows/installation_instructions.md