Add step to add `apollo.config.js`

[cheapsteak]

Have had a few intercom users saying they ran npx apollo service:check && npx apollo service:push and got Error: No service found to link to Engine

The tutorial page doesn't currently mention anything about configs

https://www.apollographql.com/docs/tutorial/production.html

There are docs for service settings from the apollo-tooling readme that can be used as reference - https://github.com/apollographql/apollo-tooling#service-settings

Related: https://github.com/apollographql/apollo-tooling/issues/771