add instructions for nested lists

Especially permutations of bulleted inside number etc. and nested ordered list using letters. How many spaces indentation are required?

1. one
1. two
1. Ay
1. Bee
1. this
2. that
1. Cee
1. three

Start by locating the repository's existing list or formatting guidance. Add instructions and examples covering mixed bulleted and numbered lists, nested ordered lists using letters, and the required indentation; done means the examples answer how many spaces each nesting level needs.

Written by the indexing model from the issue text.