Add shared config to AcceptanceCase in README
Add shared config to AcceptanceCase in README

Manually checking out connections currently doesn't work for things like making a query from a `FooChannel.join` callback or a background job so you can't run your tests async in these cases. Having the `unless tags[:async]` bit in the AcceptanceCase matches what Phoenix does and allows you to quickly toggle between async and sync when you run into this.
keathley/wallaby,aaronrenner/wallaby,aaronrenner/wallaby,keathley/wallaby