Documents in demo site

[thibaudcolas]

Follow-up to #175. We’d like one or two documents in the demo site’s content, so we can demonstrate and test the basics of how documents work in Wagtail. The documents don’t necessarily need a very bespoke integration – just having the files in the Documents library would be enough to support all we cover in our guide documentation on documents. Adding a document link in rich text would also be nice.

Discussing this on Slack in #bakerydemo, there was interest for two options:

• Having a PDF related to the site being a demo on the "About" page
• Having a "here’s a similar recipe (PDF)" link on a recipe page

Personally I’m leaning towards the latter but open to alternatives.

Recipes

Conveniently, our recipes come from Wikibooks, which already offer PDF exports of their content. Bottom left, "Download as PDF":

• https://en.wikibooks.org/wiki/Cookbook:Southern_Cornbread
• https://en.wikibooks.org/wiki/Cookbook:Hot_Cross_Bun
• https://en.wikibooks.org/wiki/Cookbook:Mincemeat_Tart

[Stormheg]

I've added two recipe pdf documents in #438