Update distance docs

[rowanwins]

Please fill in this template.

• Use a meaningful title for the pull request. Include the name of the package modified.
• Have read How To Contribute.
• Run npm test at the sub modules where changes have occurred.
• Run npm run lint to ensure code style at the turf module level.

Update the doco for turf.distance to communicate that it also accepts a Point

Resolves #2031