[Documentation] Include the link to the policy configuration example in command help

Include the link to the policy configuration file format available here - https://docs.microsoft.com/en-us/azure/devops/cli/policy-configuration-file?view=azure-devops#create-a-policy-configuration-file in the `az repos policy create` command help

In `az repos policy create` for
`--config --policy-configuration` - Local file path for configuration file. Please use / backslash when typing in directory path. **Refer the documentation [here](https://docs.microsoft.com/en-us/azure/devops/cli/policy-configuration-file?view=azure-devops#create-a-policy-configuration-file) to learn more about creating a policy configuration file.**

https://github.com/Azure/azure-cli-extensions/issues/1395 for reference