Make index.html page

This PR makes an index.html page that links to your slides, markdown file, and GitHub repo for the talk. If you merge this PR and make a new branch called gh-pages, this webpage will be available at http://mattsayler.github.io/Maptime-Impostor-Syndrome-Preso (which is case-sensitive). Then you can link to your slides on the web! Let me know if you have any questions or need any help on this.