Documentation clarification

[bgmonroe]

First and foremost, thank you so much for this provider!
The behavior of the provider to send in the existing state JSON as stdin to the spawned shell is neither explicitly nor implicitly mentioned in the provider's documentation. It took looking at examples (both in this repo as well as another) to realize what is happening. I'm not sure if this is an artifact of the larger Terraform provider architecture of specific to the shell provider (I don't really know the go language) but it's an especially useful bit of knowledge for the shell provider in particular so I think it should be called out explicitly in the provider's documentation.
Thanks,
--Brett

[Nyariki]

This should be added to the documentation.