Adds illustration credits

Author: JoseAlcerreca

README.md

@@ -1,6 +1,6 @@
 # Android Architecture Blueprints v2
 <p align="center">
-<img src="https://github.com/googlesamples/android-architecture/wiki/images/aab-logov2.png" alt="Android Architecture Blueprints"/>
+<img src="https://github.com/googlesamples/android-architecture/wiki/images/aab-logov2.png" alt="Illustration by Virginia Poltrack"/>
 </p>
 
 Android Architecture Blueprints is a project to showcase different architectural approaches to developing Android apps. In its different branches you'll find the same app (a TODO app) implemented with small differences.