change --target-path to --target_path

The target path argument should be with an underscore (at least in version: 0.1.68)

Also, I would find it useful to say a bit more about common/expected arguments for "--name". It's not clear what this could should be.

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#### Document Details

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* ID: 60c99b13-9888-31ac-9e22-4bac0cb3956a
* Version Independent ID: 7aef098d-0f55-e080-cce4-91ad6265d974
* Content: [az ml datastore](https://docs.microsoft.com/en-us/cli/azure/ext/azure-cli-ml/ml/datastore?view=azure-cli-latest#ext-azure-cli-ml-az-ml-datastore-upload)
* Content Source: [latest/docs-ref-autogen/ext/azure-cli-ml/ml/datastore.yml](https://github.com/MicrosoftDocs/azure-docs-cli/blob/live/latest/docs-ref-autogen/ext/azure-cli-ml/ml/datastore.yml)
* GitHub Login: @rloutlaw
* Microsoft Alias: **routlaw**