Adding instructions for building workshop websites.

1. Import and simplify instructions from the `swcarpentry/bc` repository.
2. Rearrange keys in YAML header of `index.html` to be in the same order as the points listed in `README.md`.
Fixing typos - thanks, @r-gaia-cs
Merge pull request #6 from gvwilson/updating-setup-instructions

Updating setup instructions