Update README and out-of-date docs

[andreyvelich]

As part of our effort to put all docs on kubeflow.org website, I made the following changes to the README and docs:

• Move adopters, roadmap, and contributing guide to the root directory.
• Remove tfjob and testing guides from docs, since they are out-of-date and not maintained.
• I will create an issue to move Prometheus monitoring docs to the website.
• For the release and proposals @kubeflow/wg-training-leads do we want to move them to the root as well ?
  • I moved existing proposals under appropriate KEP directory.
• For the README I made these updates
  • Update description, similar to the website.
  • Refer to the Kubeflow installation. @kubeflow/wg-training-leads Do we want to keep installation steps in the README or we can just link users to the website guide ?
  • Remove the very old version < 1.4 release of Training Operator, since we migrated to the unified operator 3 years ago.
  • Remove all-in-one proposal from the README.

/hold for review
cc @kubeflow/wg-training-leads @franciscojavierarceo @StefanoFioravanzo @hbelmiro Please let me know what do you think.

[coveralls]

Pull Request Test Coverage Report for Build 10777559413

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

---

Totals
Change from base Build 10739885471:	0.0%
Covered Lines:	46
Relevant Lines:	46

---

💛 - Coveralls

[franciscojavierarceo]

Suggested change

	to quickly create your first distributed training job using Python SDK.
	to quickly create your first distributed training job using the Python SDK.

[franciscojavierarceo]

Nice!

[franciscojavierarceo]

lgtm! one small nit

[tenzen-y]

Thanks
/lgtm
/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: franciscojavierarceo, tenzen-y

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [tenzen-y]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[andreyvelich]

Thanks for the review!
/hold cancel