Please add section to install the extension.

It was not immediately obvious that you needed to install the image-copy-extension to have this command at the ready in the CLI. Is it possible to add a section that addresses this and gives you "az extension add -n image-copy-extension"?

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#### Document Details

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* ID: 1806a2fb-e007-03d5-ac2d-277da130d29b
* Version Independent ID: f8583594-0ed8-ff4d-33a8-2f7c9f41c288
* Content: [az image](https://docs.microsoft.com/en-us/cli/azure/ext/image-copy-extension/image?view=azure-cli-latest#feedback)
* Content Source: [latest/docs-ref-autogen/ext/image-copy-extension/image.yml](https://github.com/MicrosoftDocs/azure-docs-cli/blob/live/latest/docs-ref-autogen/ext/image-copy-extension/image.yml)
* Service: **virtual-machines**
* GitHub Login: @rloutlaw
* Microsoft Alias: **routlaw**