Add "Edit this page button" on docs

[raybellwaves]

Proposed change

On the docs add an "Edit this page button" similar to that for ztjh (bottom right of screen shot below)

e.g. ztjh:
https://zero-to-jupyterhub.readthedocs.io/en/latest/kubernetes/amazon/step-zero-aws.html

e.g. tljh:
https://tljh.jupyter.org/en/latest/install/amazon.html

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[MridulS]

This was fixed in #840 and the "Edit" button works fine on tljh too.