Autorest: Add command line help for your generator

[olydis]

With upcoming AutoRest, there will finally be a nice, extensible CLI help available if you do --help:

The indicated part only shows when you add --csharp to the same command line, so we won't throw documentation for 8 generators and x validation tools at you at once.
All of you own a generator, so please add your part of the picture, i.e. document any flag or setting that makes your generator behave differently! Most likely, you can start with C# and just remove some stuff, since C# has a pretty wild set of stuff (except package-version and such).

The best part is, it's super easy!!!

Just add a section like this to your generator's README.md. As specified right there, the type of that YAML blob is defined here, but you may not even have to look at that. That's it.

Testing

To test, install autorest@preview and run autorest --help --use=<path to your generator>

[lmazuel]

Done for Python: https://github.com/Azure/autorest.python/pull/24

[lmazuel]

@olydis seems "clear-output-folder" is missing from "Core Settings" help right?

[marstr]

Tracking this work for Go in issue Azure/azure-sdk-for-go#2798

[RikkiGibson]

Tracking in Azure/autorest.typescript#295