Gavel and Gather Town instructions and setup

[sgbaird]

I ran into an issue with verifying an API key using sendgrid code, but per https://stackoverflow.com/a/38730585/13697228, hardcoding worked when testing with cURL. So, it was just an issue with somewhat confusing docs.

Settings when using deploy to heroku button on Gavel readme:

Set TIMEOUT to low value, typically. Depends on # of judges I guess (but idea is to not overwhelm a particular project with many judges at once).

WIP