Initial thoughts on an introductory screencast

Docs sites are so 2013. Let's start making short, simple screencasts around each feature in Jekyll to facilitate Jekyll's use. Potential topics:

- Posts
- Pages
- Pagination
- Markdown converters
- Data files
- Plugins
- Eventually Sass, CoffeeScript & Collections

*etc.*

/cc @jekyll/outreach @troyswanson