Show example.ipynb on Google Colab

[MaxGhenis]

Haven't tried it yet, but may be similar to how it's done on Tax-Calculator (notebook).

[jdebacker]

The Tax-Brain Jupyter Book now contains example.ipynb. There is an option to open in Binder right now, but not Colab.

@MaxGhenis This could be added, but is it useful if one needs to remember to install taxbrain in the notebook before running? I suppose you can add some if colab... install taxbrain type statement at the beginning... I see you have the option of a Colab notebook for microdf. Thoughts on this issue?