[Feature] Guide - Custom Domains

# **Feature Request**

## **Is your feature request related to a problem? Please describe.**

Create a new guide in the documentation that details Custom Domains

## **Describe the solution you'd like**

Custom domains can be set up using the `config` options

The installation instructions under https://astro.cloudinary.dev/installation details some of the configuration

This can also be done with the config object

https://astro.cloudinary.dev/cldimage/configuration#configuration--delivery

under `config`

Please point out some of the basics of how this would need to be set up in Cloudinary: https://support.cloudinary.com/hc/en-us/articles/202520562-Can-we-deliver-our-assets-using-a-subdomain-of-our-own-domain-like-cdn-example-com