Decide on approach and requirements for documentation

Currently HMCI is severely lacking documentation.

Some discussion has already been had around what documentation should be provided, this can roughly be broken down into 3 categories:

**Code documentation**
Most of the code is doc blocked, but has missing/incorrect @param and @return types and descriptions

**Example implementations**
Developers should have a library of example implementations to use as foundations for their work. We have an issue open for this, as well as a list of projects which we have used HMCI here:
https://github.com/humanmade/hm-content-import/issues/61
https://docs.google.com/document/d/1aAr9RVz9YGLtzyo9NBeegEbjgISuYzvL7eXpPQpOYjI/edit#

**Best practices/approaches to content migration**
This would primarily involve documentation on general considerations and approaches to take when working on a content migration. e.g.
- How to handle redirects
- How to handle rich content manipulation (replacing images/links etc)
- How to run imports on HM hosting https://docs.google.com/document/d/19h1huZXefIprVg23zQHYRcps5esYV7_GzkExZjhUT6s/edit?usp=sharing
- What data to store and how
- How to ensure imports are properly logged
- How to manage delta imports
- How to manage manual editorial modification of imported content (particularly when delta imports are involved)

**Actionables**
- Developers to discuss and provide input on where and how to work on documentation