Add GitHub Pages for pkgdown

[geanders]

I don't think we're serving the pkgdown pages anywhere yet. I think we'll need to set up GitHub Pages to enable that.

[geanders]

We can build the site locally using:

pkgdown::build_site()

This renders the documentation to a "docs" folder in the package. I committed these and pushed them to GitHub.

From the "Pages" section of the "Settings" in the repo, I think it's being built from what we pushed in the docs folder.

[geanders]

I think we won't see these until we merge the devel branch back into the master branch

[geanders]

I'm switching GitHub Pages to use the devel branch for the moment, so we can check it online, but we'll want to change this back so it pulls from the master branch before we submit to CRAN.

The link for the pkgdown documentation is:

http://geanders.github.io/noaastormevents/