docs: add link to userguide and specify install @next

Author: lpatiny

README.md

@@ -9,14 +9,19 @@ Image processing and manipulation in JavaScript.
 
 ## Installation
 
-`$ npm i image-js`
+`$ npm i image-js@next`
 
 ## [API](https://image-js.github.io/image-js-typescript/)
 
 ## Development
 
 See [Development documentation](./Development.md).
 
+## Userguide
+
+See [https://image-js-docs.pages.dev/docs/Getting%20started](https://image-js-docs.pages.dev/docs/Getting%20started)
+
+
 ## License
 
 [MIT](./LICENSE)