Readme for language plugins with specific info for SDK projects and features

Feature Request

Describe the problem you need a feature to resolve.

For Golang we scaffold a Readme file, see: https://github.com/kubernetes-sigs/kubebuilder/pull/2610
I think it would be nice if we have the same for the other languages.

Additionally, wdyt about we have a helper plugin that adds on top the steps specific for SDK and how to test the bundle with the operator-sdk run bundle.

Describe the solution you'd like.

a) Ensure that we are OK with the default README scaffold via Kubebuilder ( see if we would like not to improve or change it first )
b) Then use this README as a base to create a template for all language plugins
c) Create a new helper plugin in SDK as we have manifest/v2 (https://github.com/operator-framework/operator-sdk/tree/master/internal/plugins/manifests/v2) which does changes on top of the Makefile so that we could encourage and skill up authors and users of these projects use operator-sdk run bundle as specific and nice helpers provided by SDK.

Start by reviewing the Kubebuilder README scaffold referenced in the issue, then inspect internal/plugins/manifests/v2 and the existing Makefile changes. Define the README template needs for the language plugins and the SDK helper plugin scope. Done means language-specific README scaffolding and a helper that supports the described bundle-testing workflow.