Add documentation for the List crock

[dalefrancis88]

Description

To bring it in-line with the other Crocks we need to add in descriptive documentation for the List crock with examples

Task List

• Add main List.md file to 'docs/src/pages/docs/crocks/' based on the others
• Ensure it has the correct 'weight'
• Locate all references to List and update it to link to the new List documentation. Reference the section where possible
• Update docs/src/pages/docs/crocks/index.md with links to the new List.md page
• Update docs/src/pages/docs/functions/pointfree-functions.md with links to the new List.md page

For more information, see the CONTRIBUTING guide.

Further Information

This was sourced from #42
This will need to wait and be completed after the changes are made to the behaviour for List