Fix link to application default credentials in README files

Author: jradcliff

google-analytics-admin/README.md

@@ -9,6 +9,7 @@ These samples show how to use the
 [Google Analytics Admin API](https://developers.google.com/analytics/devguides/config/admin/v1) from Java.
 
 ## Build and Run
+
 1.  **Enable APIs** - [Enable the Analytics Admin API](https://console.cloud.google.com/flows/enableapi?apiid=analyticsadmin.googleapis.com)
     and create a new project or select an existing project.
 2.  **Download The Credentials** - Configure your project using [Application Default Credentials][adc].
@@ -35,3 +36,4 @@ These samples show how to use the
     mvn -q compile exec:java -Dexec.mainClass='com.example.analytics.QuickstartSample'
     ```
 
+[adc]: https://cloud.google.com/docs/authentication#adc

google-analytics-data/README.md

@@ -9,6 +9,7 @@ These samples show how to use the
 [Google Analytics Data API](https://developers.google.com/analytics/devguides/reporting/data/v1) from Java.
 
 ## Build and Run
+
 1.  **Enable APIs** - [Enable the Analytics Data API](https://console.cloud.google.com/flows/enableapi?apiid=analyticsdata.googleapis.com)
     and create a new project or select an existing project.
 2.  **Download The Credentials** - Configure your project using [Application Default Credentials][adc].
@@ -39,3 +40,4 @@ These samples show how to use the
     [`src/main/java/com/example/analytics`](src/main/java/com/example/analytics)
     directory.
 
+[adc]: https://cloud.google.com/docs/authentication#adc