[ROCm] Update C++ Custom Operators tutorial with note about AMD GPU.

[naromero77amd]

Fixes #ISSUE_NUMBER

Description

This is a minor update to the C++ Custom Operators with a note about AMD GPU support.

Checklist

• The issue that is being fixed is referred in the description (see above "Fixes #ISSUE_NUMBER")
• Only one issue is addressed in this pull request
• Labels from the issue that this PR is fixing are added to this pull request
• No unnecessary issues are included into this pull request.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/tutorials/3198

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[svekars]

cc: @malfet @zou3519