document incident response
Created by: nicksnyder
This PR adds formal documentation for how we handle operational incidents. Recent examples where things could have been smoother:
- https://sourcegraph.slack.com/archives/C07KZF47K/p1551109950081000
- https://sourcegraph.slack.com/archives/C07KZF47K/p1550635082100300
- https://sourcegraph.slack.com/archives/C07KZF47K/p1550864121040800
- https://sourcegraph.slack.com/archives/C08JA8Q1H/p1551802827040800
I am also planning to rename #dev-ops to #incidents. The #incidents channel with be solely dedicated to discussing important incidents. Any non-incident conversations that happened in #dev-ops previously can move to #dev-chat.