Add frameworkcontroller document

[SparkSnail]

1. Add frameworkcontroller document.
2. Fix other document small issues.

[PurityFan]

LGTM!

[yqwang-ms]

Can we refer kubeflow doc as fewer as possible? It is better to refer a common k8s doc instead of kubeflow doc 😆

Besides, what is the doc to support other frameworks except for tf? And it would be better if we can mention the strength that frameworkcontroller can support all these frameworks.

And what is the plan to add the related project frameworkcontroller and the how-to in the nni project home readme? :)

[yqwang-ms]

BTW, I see you added the frameworkcontroller's framework crd. By design, it will be created by frameworkcontroller itself, so frameworkcontroller's user, such as nni, shouldn't care about it. So, I wonder why you need maintain the crd file in nni project?

[SparkSnail]

@yqwang-ms Thanks for your comment. The docs about kubeflow is https://github.com/Microsoft/nni/blob/dev-doc/docs/KubeflowMode.md, there is only tf operator doc now, pytorch operator will be added to this doc. I will update the doc as you suggested, and update the pr.
As for "add the related project frameworkcontroller ", we will discuss the plan in meeting, and it will be added soon.
I add crd file in project because nni use ts kubernetes rest client, and the code need to use crd template to create job.

[yqwang-ms]

Got it :)
And seems currently you only support single machine training, so why not directly support distributed training? (to support it you need to use frameworkbarrier and enable fancyRetryPolicy, see https://github.com/Microsoft/frameworkcontroller/blob/master/example/framework/scenario/tensorflow/cpu/tensorflowdistributedtrainingwithcpu.yaml)