Documentation correction

[Mykyta-Chernenko]

Thank you for a great template, I am using https://github.com/codingki/react-native-expo-template/tree/master/template-typescript-bottom-tabs-supabase-auth-flow.

There is a little part that is incorrect in the docs
// Better put your these secret keys in .env file

supabaseUrl and supabaseKey are both non-secret values. And if they were, it would still not help much. There are kind of no secret values in mobile development