added example to terraform state list documentation

[FloxD]

Added an example on how to perform terraform state list when there's an index in the resource address.
Added this because you need to use single quotes to make this work and none of the existing examples include those.

[hashicorp-cla-app]

All committers have signed the CLA.

[hashicorp-cla-app]

Thank you for your submission! We require that all contributors sign our Contributor License Agreement ("CLA") before we can accept the contribution. Read and sign the agreement

Learn more about why HashiCorp requires a CLA and what the CLA includes

---

FloxD seems not to be a GitHub user.
You need a GitHub account to be able to sign the CLA.
If you have already a GitHub account, please add the email address used for this commit to your account.

_{Have you signed the CLA already but the status is still pending? Recheck it.}

[crw]

This seems reasonable, I'll add it to the queue to review. Thanks!