Increase docs clarity

[forsyth2]

Summary

Objectives:

• Add tests confirming expected behavior in various tar workflows (originally Add test of tar workflows #418).
• Update documentation (based on scenarios unit/integration tested) to answer FAQ about zstash behavior.

Issue resolution:

• Replaces Add test of tar workflows #418 as resolution for discussion Can `zstash` transfer tars without extracting? #417

Select one: This pull request is...

• a bug fix: increment the patch version
• a small improvement: increment the minor version
• a new feature: increment the minor version
• an incompatible (non-backwards compatible) API change: increment the major version

Small Change

• To merge, I will use "Squash and merge". That is, this change should be a single commit.
• Logic: I have visually inspected the entire pull request myself.
• Pre-commit checks: All the pre-commits checks have passed.

[forsyth2]

Commit 3 addresses the user question in #401 as well.

[forsyth2]

Action items:

• Visually inspect test/doc changes and evaluate their accuracy.
• Code review