Clarify stimzx readme (#217)
Clarify stimzx readme (#217)

- Note that it's not a published package so has to be installed from source
- Fix one of the examples having the wrong output
- Add s state distillation as an example
quantumlib/Stim,quantumlib/Stim,quantumlib/Stim,quantumlib/Stim,quantumlib/Stim,quantumlib/Stim