List component should support nested list items

[silvalaura]

Describe the bug Our List component should support nested list items:

<List isOrdered={true}>
        <ListItem>List content</ListItem>
        <ListItem>List content</ListItem>
        <List>
          <ListItem>1 Nested List content</ListItem>
        </List>
        <List>
          <ListItem>2 Nested List content</ListItem>
        </List>
        <ListItem>List content</ListItem>
      </List>

To Reproduce Steps to reproduce the behavior:

1. Go to https://codesandbox.io/s/rm-list-8u97jo?file=/example.tsx
2. Notice that nested lists are not supported

Expected behavior Nested lists should work similarly to native lists

Screenshots

Notes Let's add an example of nested lists to the docs site

[silvalaura]

Relates to #413

[orion-cengage]

I verified the updated component works and looks as expected and I like the accompanying updates to the docs.