Small documentation update

Please don't mind the amount of commits for this pull request, my brain is failing this morning.

The change from 'sample app' to 'example app' was made due to the name of the repo name https://github.com/flightjs/example-app. I was going to suggest to add a link to that as well, but didn't know if it would flow with the rest of the information.

The README added to the doc directory allows for an easier reading experience on Github. It may be a good idea to add little descriptions to those links, but again, I didn't find a good way at the moment to make that look/read nice.