Write Docs on How To Add A Feature/Functionality

[TTWNO]

Steps are roughly:

• Find event that corresponds to the desired feature
• Decide if there are any pre-requisites to the feature being triggerwd (think: focused window only, open tab only, etc.)
• See if the prerequisite is already defined (we have some for only focused window events for example)
• Decide what, if any, state is required for your feature (caret position, last focused item, etc.)
• Check to see if we already have your state info as a type (if not, make a newtype and implement FromAsyncState for it)
• Implement a new function that takes PreRequisiteType<EventType>, and StateType. That function can retuen a list of Commands that Odilia will act on.