Enhance Jira Core documentation on the Default Issue Type Scheme

There doesn't appear to be much information in regards to what issue types should be automatically added to the Default Issue Type Scheme.

This has led to some confusion by a recent customer I worked with. I predict that we may see similar issues raised like this in the future. 

While researching how we should expect the Default Issue Type Scheme to work, I found the following quote from JRASERVER-59866:

The behavior of the default issue type scheme in JIRA 7.0 and up is intentional and documented. As our documentation says "new issue type will be automatically added to the Default Issue Type Scheme". This does not mean that all issue types in JIRA, especially those defined in project blueprints from JIRA Software, JIRA Service Desk, and JIRA Core will automatically be added to the Default Issue Type Scheme.

It would be great to either create a new Data Center documentation page specific to the Default Issue Type Scheme or, perhaps add further details to the following Jira Cloud documentation (and duplicate them for Jira Core, etc.):

What are issue type schemes?
Add, edit, and delete an issue type