fix: Add instructions to installation section in docs

Author: haroldadmin

docs/docs/docs/index.md

@@ -58,14 +58,23 @@ allprojects {
 }
 ```
 
-And then add the dependency in your gradle file:
+Then add the dependency in your gradle file:
 
 ```groovy
 dependencies {
   implementation "com.github.haroldadmin:NetworkResponseAdapter:(latest-version)"
 }
 ```
 
+And finally, register `NetworkResponseAdapter` with Retrofit:
+
+```kotlin
+val retrofit = Retrofit.Builder()
+ .addCallAdapterFactory(NetworkResponseAdapterFactory())
+ ... // Other config
+ .build()
+```
+
 <!-- prettier-ignore-start -->
 !!! note
     This library uses OkHttp 4, which requires Android API version 21+ and Java 8+.