[Android]add serverUrl documentation (#1338)

Author: krunalsshah

docs/api-android.md

@@ -18,6 +18,8 @@ Constructs the CodePush client runtime and represents the `ReactPackage` instanc
 
 - __CodePush(String deploymentKey, Context context, boolean isDebugMode, Integer publicKeyResourceDescriptor)__ - Equivalent to the previous constructor, but allows you to specify the public key resource descriptor needed to read public key content. Please refer to [Code Signing](setup-android.md#code-signing) section for more details about Code Signing Feature.
 
+- __CodePush(String deploymentKey, Context context, boolean isDebugMode, String serverUrl)__ Constructor allows you to specify CodePush Server Url. The Default value: `"https://codepush.azurewebsites.net/"` is overridden by value specfied in `serverUrl`. 
+
 ##### Builder
 
 As an alternative to constructors *you can also use `CodePushBuilder`* to setup a CodePush instance configured with *only parameters you want*.
@@ -30,6 +32,7 @@ As an alternative to constructors *you can also use `CodePushBuilder`* to setup
             new CodePushBuilder("deployment-key-here",getApplicationContext())
                 .setIsDebugMode(BuildConfig.DEBUG)
                 .setPublicKeyResourceDescriptor(R.string.publicKey)
+                .setServerUrl("https://yourcodepush.server.com")
                 .build() //return configured CodePush instance
       );
     }