migrate site content: contributing docs (#4709)

* migrate contributing docs

* modifies weight for ordering

* updates links and info based on feedback

* removes broken powershell link

* Update site/content/en/contribute/windows/_index.md

Co-authored-by: Katrina Verey <kn.verey@gmail.com>

* Update site/content/en/contribute/windows/_index.md

Co-authored-by: Katrina Verey <kn.verey@gmail.com>

* Update site/content/en/contribute/mac/_index.md

Co-authored-by: Katrina Verey <kn.verey@gmail.com>

* Update site/content/en/contribute/howitworks/_index.md

Co-authored-by: Katrina Verey <kn.verey@gmail.com>

* Update site/content/en/contribute/howitworks/_index.md

Co-authored-by: Katrina Verey <kn.verey@gmail.com>

* simplify build explanation

* removes windows docs

* removes community - duplicate

* update the tooling instructions

* point to proposal docs

* Update site/content/en/contribute/howitworks/_index.md

Co-authored-by: Katrina Verey <kn.verey@gmail.com>

site/content/en/contribute/howitworks/_index.md

@@ -0,0 +1,26 @@
+---
+title: "Writing Code"
+linkTitle: "Writing Code"
+type: docs
+weight: 40
+description: >
+    Background information to help orient newcomers to the Kustomize codebase
+---
+
+{{< alert color="success" title="Workspace mode" >}}
+Kustomize supports go workspace mode, so if adding locally modified modules, remember to also add it to the [go.work](https://github.com/kubernetes-sigs/kustomize/blob/master/go.work) file.
+
+{{< /alert >}}
+
+#### Build command
+
+All kustomize commands can be found in [kustomize/commands](https://github.com/kubernetes-sigs/kustomize/tree/master/kustomize/commands)
+
+Running `kustomize build` triggers the [NewCmdBuild](https://github.com/kubernetes-sigs/kustomize/blob/master/kustomize/commands/build/build.go#L65), which does the following:
+
+- creates a [Kustomizer](https://github.com/kubernetes-sigs/kustomize/blob/master/kustomize/commands/build/build.go#L77) instance
+
+- calls [Run](https://github.com/kubernetes-sigs/kustomize/blob/482e8930fc256672afd4ff5d531ec8fe80d35119/api/krusty/kustomizer.go#L53-L543)  to perform the kustomization
+
+- returns the [kustomization output as yaml](https://github.com/kubernetes-sigs/kustomize/blob/master/kustomize/commands/build/build.go#L89-L97)
+