lark: event docs

Fixes: #55 (closed)

Local Checklist

• Read our Contributing guide (for newcomers)
• Tests written and passing locally?
• Code style checked?
• QA-ed locally?
• Rebased with master branch?
• Configuration updated (if needed)?
• Documentation updated (if needed)?

What does this Merge Request do?

Expands the README.md substantially. Adds an EVENT_LOG.md which begins to specify the formal requirements for the event log.

Why are we doing this? Any context of related work or Epic?

References #55 (closed)