Link to retrieve raster tiles from styles docs

[lizziegooding]

Link to API docs so it's clear which API endpoint these methods are using.

cc @mollymerp @bsudekum

Next steps

• [x] review by @mollymerp
• [ ] review by @danswick
• [x] @lizziegooding address feedback
• [ ] merge!

[lizziegooding]

Thank you for the review @mollymerp 🚀