[facilitator guide] Create facilitator guide for postmortem exercise

[tylerauerbeck]

📝 Description

We should make sure to have documentation highlighting the key components we want to enfoce within our postmortem exercise

✅ A/Cs

• Reiterate the importance of a blameless postmortem.
• Underling the importance of learning from both the problem itself as well as the way the team reacted to it
• Highlight the importance of having defined action items coming out of this to address the original problem and events that came about after it occurred.