doc: add plugins contribution doc (#4732)

Signed-off-by: Camila Macedo <cmacedo@redhat.com>

website/content/en/docs/contribution-guidelines/plugins.md

@@ -0,0 +1,80 @@
+---
+title: Plugins
+linkTitle: Plugins
+weight: 7
+---
+
+## Overview
+
+SDK uses the project [Kubebuilder][kubebuilder] as a library for the CLI and plugins features. For further information see the [Plugins][kb-plugins-doc] document. To better understand its motivations, check the design documentation [Integrating Kubebuilder and Operator SDK][kb-int-sdk].
+
+## SDK Language-based plugins
+
+All language-based operator projects provided by SDK (Ansible/Helm/Golang) follow the Kubebuilder standard and have a common base. The common base is generated using [kustomize][kustomize] which is a project maintained and adopted by Kubernetes community to help work with the Kubernertes manifests (YAML files) that are used to configure the resources on the clusters.
+
+The specific files for each language are scaffolded for the language's plugins. The Operator SDK CLI tool can provide custom plugins and helpers which are common and useful for all language types. To check the common base, you can also run:
+
+```sh
+operator-sdk init --plugins=kustomize
+```
+
+Also, see the topic [Language-based Plugins][kb-language-plugins] to understand how it works.
+
+### Common scaffolds 
+
+Following the default common scaffolds for the projects which are built with SDK.
+
+| File/Directory | Description | 
+| ------ | ----- |
+|  Dockerfile |  Defines the operator(manager) image |  
+|  Makefile |  Provides the helpers and options for the users. (e.g. `make bundle` which generate/update the OLM [bundle][bundle] manifests ) |  
+|  PROJECT |  Project configuration. Stores the data used to do the scaffolds. For further information see [Project Config][kb-project] | 
+|  bundle.Dockerfile | Docker image which is used to provide the helpers to integrate the project with OLM. (e.g. [operator-sdk run ./bundle][sdk-cli-run-bundle]) | 
+|  config/ |  Directory which has all [kustomize's][kustomize] manifest to configure and test the project | 
+
+You can check the [Project Layout][project-layout] to better understand the files and directories scaffolded by SDK CLI, which may be common for each language-type.
+
+## Custom Plugins
+
+By default plugins are used by the Operator SDK to provide the following features:
+
+- [manifests.sdk.operatorframework.io][plugin-manifest]: perform the required scaffolds to provide the helpers to allow the projects to be integrated with OLM. 
+- [scorecard.sdk.operatorframework.io][plugin-scorecard]: perform the required scaffolds to provide the [Scorecard][scorecard] feature.
+
+### Optional/custom plugins
+
+Users can also use custom plugins when they execute the SDK CLI sub-commands as a helper which includes the following options:
+
+```sh
+operator-sdk create api --plugins="go/v3,declarative"
+```
+
+The above example will scaffold custom code in the controllers after an API is created to allow the users to develop solutions using the [kubebuilder declarative pattern][kubebuilder-declarative-pattern]. (e.g [default scaffold][default-scaffold] versus [example][kubebuilder-declarative-pattern-example]).
+
+Note that custom plugins are called via the init sub-command to work as global plugins, and will be added in the `layout` field of the PROJECT file. Any sub-command executed will then also be called.
+
+## Plugins Vision
+
+Maintainers and contributors are able to create their own plugin(s) using the same standards and approaches. These contributions in the future could be added as solutions to be compatible and used with the Operator SDK CLI. Currently, the SDK cannot discover and use plugins that are not shipped or built with its binary. However, it has been discussed in the issue [kubebuilder/issues/1378][kb-issue].
+
+## How to create your own plugins
+
+If you are looking to develop similar solutions to allow users for example to create projects using other languages or that could work as helpers for the projects built with SDK/Kubebuilder projects, then see the [Creating your own plugins][create-your-own-plugins] to see how you can benefit and apply this approach.
+
+[kb-plugins-doc]: https://master.book.kubebuilder.io/plugins/plugins.html
+[kb-int-sdk]: https://github.com/kubernetes-sigs/kubebuilder/blob/master/designs/integrating-kubebuilder-and-osdk.md
+[kb-language-plugins]:https://master.book.kubebuilder.io/plugins/creating-plugins.html#language-based-plugins
+[kustomize]: https://github.com/kubernetes-sigs/kustomize
+[bundle]: https://github.com/operator-framework/operator-registry/blob/v1.16.1/docs/design/operator-bundle.md#operator-bundle
+[kb-project]: https://master.book.kubebuilder.io/reference/project-config.html
+[sdk-cli-run-bundle]: /docs/cli/operator-sdk_run
+[project-layout]: /docs/overview/project-layout
+[plugin-manifest]: https://github.com/operator-framework/operator-sdk/tree/master/internal/plugins/manifests/v2
+[plugin-scorecard]: https://github.com/operator-framework/operator-sdk/tree/master/internal/plugins/scorecard/v2
+[kubebuilder-declarative-pattern]: https://github.com/kubernetes-sigs/kubebuilder-declarative-pattern
+[kubebuilder-declarative-pattern-example]: https://github.com/kubernetes-sigs/kubebuilder/blob/master/testdata/project-v3/controllers/firstmate_controller.go
+[default-scaffold]: https://github.com/kubernetes-sigs/kubebuilder/blob/master/testdata/project-v3/controllers/admiral_controller.go
+[kb-issue]: https://github.com/kubernetes-sigs/kubebuilder/issues/1378
+[create-your-own-plugins]: https://master.book.kubebuilder.io/plugins/creating-plugins.html
+[scorecard]: /docs/advanced-topics/scorecard/scorecard/
+[kubebuilder]: https://github.com/kubernetes-sigs/kubebuilder 

website/content/en/docs/contribution-guidelines/releasing.md

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 ---
 title: Release Guide
 linkTitle: Releasing
-weight: 30
+weight: 4
 ---
 
 These steps describe how to conduct a release of the operator-sdk repo using example versions.

website/content/en/docs/contribution-guidelines/reporting-issues.md

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 ---
 title: Reporting Issues
 linkTitle: Reporting Issues
-weight: 40
+weight: 5
 ---
 
 If any part of the operator-sdk project has bugs or documentation mistakes, please let us know by [opening an issue][operator-sdk-issue]. We treat bugs and mistakes very seriously and believe no issue is too small. Before creating a bug report, please check that an issue reporting the same problem does not already exist.

website/content/en/docs/contribution-guidelines/testing.md

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 ---
 title: Testing
 linkTitle: Testing
-weight: 10
+weight: 6
 ---
 
 On all PRs, a suite of static and cluster tests is run against your changes in a CI environment.