Fix typos and spacing

…in http://origami.ft.com/docs/developer-guide/building-modules/

- Use a single type of quotes in the markup (double quotes)
- Change remaining spaces to tabs
- Fix typos
- Change src of the script to the polyfills service with the new URL
- Lowercase the message in the body (`[FIND HEADER AND FOOTER COMPONENTS FROM registry.origami.ft.com TO PUT HERE]`)