Add full working example to readme

    `NextcloudAPI` provides a method called `performNetworkRequest(NextcloudRequest request)` that allows you to handle the server response yourself.

    ```java

    // create nextcloudAPI instance

    public class MyActivity extends AppCompatActivity {

        NextcloudAPI mNextcloudAPI;

        @Override

        protected void onStart() {

            Account account = SingleAccountHelper.GetCurrentAccount(context);

            SingleSignOnAccount ssoAccount = AccountImporter.GetAuthTokenInSeparateThread(context, account);

    NextcloudAPI nextcloudAPI = new NextcloudAPI(context, ssoAccount, GsonConfig.GetGson(), callback);

            mNextcloudAPI = new NextcloudAPI(context, ssoAccount, GsonConfig.GetGson(),  new NextcloudAPI.ApiConnectedListener() {

                @Override

                public void onConnected() {

                    downloadFile();

                }

                @Override

                public void onError(Exception ex) {

                    // TODO handle error here..

                }

            });

        }

        @Override

        protected void onStop() {

            // Close Service Connection to Nextcloud Files App and

            // disconnect API from Context (prevent Memory Leak)

            mNextcloudAPI.stop();

        }

        private void downloadFile() {

            NextcloudRequest nextcloudRequest = new NextcloudRequest.Builder()

                    .build();

            try {

            InputStream inputStream = nextcloudAPI.performNetworkRequest(nextcloudRequest);

                InputStream inputStream = mNextcloudAPI.performNetworkRequest(nextcloudRequest);

                while(inputStream.available() > 0) {

                    inputStream.read();

                    // TODO do something useful with the data here..

                e.printStackTrace();

            }

        }

    }

    ```

## Video