Add note about iOS ATS settings to README

Author: jevakallio

README.md

@@ -79,7 +79,7 @@ with optional overrides.
 * **additionalParameters** - (`object`) additional parameters that will be passed in the authorization request.
   Must be string values! E.g. setting `additionalParameters: { hello: 'world', foo: 'bar' }` would add
   `hello=world&foo=bar` to the authorization request.
-* **dangerouslyAllowInsecureHttpRequests** - (`boolean`) _ANDROID_ whether to allow requests over plain HTTP or with self-signed SSL certificates. :warning: Can be useful for testing against local server, _should not be used in production._
+* :warning: **dangerouslyAllowInsecureHttpRequests** - (`boolean`) _ANDROID_ whether to allow requests over plain HTTP or with self-signed SSL certificates. Can be useful for testing against local server, _should not be used in production._ This setting has no effect on iOS; to enable insecure HTTP requests, add a [NSExceptionAllowsInsecureHTTPLoads exception](https://cocoacasts.com/how-to-add-app-transport-security-exception-domains) to your App Transport Security settings.
 
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