How to do strikethrough in a reStructuredText file hosted on GitHub?

Not so clean solution, but works for me.

.. raw:: html

   <s>

This text is crossed out

.. raw:: html

   </s>

You can also use substitutions to make multiple uses easier. Put this markup somewhere in your file:

.. |ss| raw:: html

   <strike>

.. |se| raw:: html

   </strike>

Then just enclose the text to be struck out with |ss| & |se|:

One, |ss| two |se|, three |ss| strikes |se| you're out!

will render as:

One, two , three strikes you're out!

Just be sure to have space around the substitution elements, so they are parsed correctly. It looks a bit awkward here, but this is a contrived example.