Improve doc comments on WithVolume & WithBindMount

[DamianEdwards]

Description

Improves the doc comments for the WithVolume and WithBindMount methods based on user feedback.

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
• Are you including unit tests for the changes and scenario tests if relevant?
  • n/a
• Did you add public API?
  • No
• Does the change make any security assumptions or guarantees?
  • No
• Does the change require an update in our Aspire docs?
  • Yes
    • Is this introducing a breaking change?
      • No
    • Link to aspire-docs issue: Update docs for volumes docs-aspire#2699

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