📖 Improve root README.md

[furkatgofurov7]

What this PR does / why we need it:
Improves a bit root level README.md document with:

• removing:
  • generic notes from the scaffolding of the repo
  • link to k8s dev mailing list (please let me know this, happy to link to operator specific mailing list if there is any, but I am not aware of)
• adds proper link to the operator slack channel

Mainly inspired by the Cluster API repo notes :)

[furkatgofurov7]

/cc @Fedosin

[damdo]

/lgtm
Thanks!

[Fedosin]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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[furkatgofurov7]

This is to test kubernetes/test-infra#29664:

/cherry-pick release-0.2

[k8s-infra-cherrypick-robot]

@furkatgofurov7: new pull request created: #127

In response to this:

This is to test kubernetes/test-infra#29664:

/cherry-pick release-0.2

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[furkatgofurov7]

@furkatgofurov7: new pull request created: #127

It seems to work, closing the cherry-pick PR.