bit.ly/learn-xls and bit.ly/xls-playground should be served from the canonical github repo

currently it's a weird mix of:
- colab saved on gist.github.com
- bootleg wheel downloaded https://github.com/proppy/xls/releases

instead it should be served from https://github.com/google/xls using [colab github integration](https://colab.sandbox.google.com/github/googlecolab/colabtools/blob/master/notebooks/colab-github-demo.ipynb) and tested w/ GitHub workflows (similar to what's being done w/ https://github.com/chipsalliance/silicon-notebooks/tree/main/.github/workflows