Add firebase config ktx in readme

Author: Eduard Ablekimov

readme.MD

@@ -61,6 +61,7 @@ implementation "cz.ackee.updatechecker:firebase-fetcher:x.x.x"
 Besides that, you need to add a dependency to the Firebase Remote Config since it is not transitive.
 ```groovy
 implementation "com.google.firebase:firebase-config:x.x.x"
+implementation "com.google.firebase:firebase-config-ktx:x.x.x"
 ```