Updated README

Author: nthiery

README.md

@@ -1,11 +1,14 @@
 # test-binder-sage: Testing binder services for deploying SageMath Jupyter notebooks
 
-[![Binder](http://mybinder.org/badge.svg)](http://mybinder.org:/repo/nthiery/test-binder-sage/)
+[![Binder](https://beta.mybinder.org/badge.svg)](https://beta.mybinder.org/v2/gh/nthiery/test-binder-sage/master)
 
 ## Authors
 
 Nicolas M. Thiéry
 
 ## Notebooks
 
-- [index.ipynb](index.ipynb): starter notebook
+- [index.ipynb](index.ipynb): starter notebook / brief SageMath demo
+- [demo-gap.ipynb](index.ipynb): GAP brief demo
+- [demo-pari.ipynb](index.ipynb): Pari/GP brief demo
+- [demo-singular.ipynb](index.ipynb): Singular brief demo