K8SPG-569 remove upstream docs and add reamde

[fiowro]

CHANGE DESCRIPTION

Problem: docs/ directory contains docs merged from upstream (actually, the upstream website) which are often not applicable to our code

Cause: It’s confusing, because some users think that’s are our docs

Solution: These upstream docs should be replaced with a readme about the actual docs placement

CHECKLIST

Jira

• [ ] Is the Jira ticket created and referenced properly?
• [ ] Does the Jira ticket have the proper statuses for documentation (Needs Doc) and QA (Needs QA)?
• [ ] Does the Jira ticket link to the proper milestone (Fix Version field)?

Tests

• [ ] Is an E2E test/test case added for the new feature/change?
• [ ] Are unit tests added where appropriate?

Config/Logging/Testability

• [ ] Are all needed new/changed options added to default YAML files?
• [ ] Are the manifests (crd/bundle) regenerated if needed?
• [ ] Did we add proper logging messages for operator actions?
• [ ] Did we ensure compatibility with the previous version or cluster upgrade process?
• [ ] Does the change support oldest and newest supported PG version?
• [ ] Does the change support oldest and newest supported Kubernetes version?

[JNKPercona]

Test name	Status
custom-extensions	failure
demand-backup	failure
init-deploy	failure
monitoring	failure
operator-self-healing	skipped
scaling	skipped
scheduled-backup	skipped
self-healing	skipped
start-from-backup	skipped
telemetry-transfer	skipped
upgrade-minor	skipped
users	skipped
We run 4 out of 12

commit: https://github.com/percona/percona-postgresql-operator/pull/733/commits/b800b5ff5b5b1c58f1f6847c222e81f552195008 image: perconalab/percona-postgresql-operator:PR-733-b800b5ff5