Update instructions to prepend 'http://' to Valid OAuth redirect URIs

[bentonwong]

The current instructions state:

'In the Valid OAuth redirect URIs field, enter localhost:3000/auth/facebook/callback...'

Student reported error when leaving out the preceding 'http://' in the address. Suggest updating it to:

'http://localhost:3000/auth/facebook/callback'

[alexisadorn]

I had a similar issue - without explicitly adding http://, Facebook Developers auto-generates it as https://

This causes an error when navigating to http://localhost:3000 and clicking on the log-in link

[curlywallst]

Same problem again. Facebook now requires a secure server and localhost is not secure so it throws an "Insecure login blocked" error. Student tried a variety of ways to get around this but could not get around it