Add note about priority to rewrites docs (#17535)

This adds a note about public files and pages taking higher priority over rewrites causing them to not be able to be rewritten unless the files are renamed first since this has been asked a few times. 

x-ref: #17513
x-ref: #9081 (comment)
x-ref: #9081 (comment)

docs/api-reference/next.config.js/rewrites.md

@@ -17,6 +17,8 @@ Rewrites allow you to map an incoming request path to a different destination pa
 
 Rewrites are only available on the Node.js environment and do not affect client-side routing.
 
+Rewrites are not able to override public files or routes in the pages directory as these have higher priority than rewrites. For example, if you have `pages/index.js` you are not able to rewrite `/` to another location unless you rename the `pages/index.js` file.
+
 To use rewrites you can use the `rewrites` key in `next.config.js`:
 
 ```js