update URL

Author: t-kalinowski

DESCRIPTION

@@ -23,7 +23,7 @@ Description: Interface to 'Keras' <https://keras.io>, a high-level neural
   combinations of the two), and runs seamlessly on both 'CPU' and 'GPU' devices.
 Encoding: UTF-8
 License: MIT + file LICENSE
-URL: https://tensorflow.rstudio.com/
+URL: https://tensorflow.rstudio.com/, https://github.com/rstudio/keras/tree/r2
 BugReports: https://github.com/rstudio/keras/issues
 Depends:
     R (>= 3.6)