Update helm3 mixin link and changed client version in docs

[troy0820]

What does this change

• Change the example link to show the helm3-mixin page by porter
• Change the helm client version in the curl command and explanation to minimum required of 3.8.2

What issue does it fix

Closes #2759

Notes for the reviewer

Checklist

• Did you write tests?
  • No changes in code butupdated documentation
• Did you write documentation?
  • Updated documentation
• Did you change porter.yaml or a storage document record? Update the corresponding schema file.
  • No
• If this is your first pull request, please add your name to the bottom of our Contributors list. Thank you for making Porter better! 🙇‍♀️

Reviewer Checklist

• Comment with /azp run test-porter-release if a magefile or build script was modified
• Comment with /azp run porter-integration if it's a non-trivial PR

[schristoff]

[schristoff]

/azp run porter-integration

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