docs: add note about globalThis.fetch fallback

README.md

@@ -37,7 +37,7 @@ const { $fetch } = require('ohmyfetch')
 ## ✔️ Works with Node.js
 
 We use [conditional exports](https://nodejs.org/api/packages.html#packages_conditional_exports) to detect Node.js
- and automatically use [node-fetch](https://github.com/node-fetch/node-fetch).
+ and automatically use [node-fetch](https://github.com/node-fetch/node-fetch). If `globalThis.fetch` is available, will be used instead.
 
 ## ✔️ Parsing Response