Reorganize docs contrib guide (#9510)

* Reorganize docs contrib guide

* Address first round of feedback from Brad, Jared

* Standardize on 'SIG Docs'

* Address more feedback

* Rewrites to participating.md

* Tweak navigation titles

* Document PR Wrangler

* Document SIG Docs chairperson

* Fix codeblock that shows how to use <codenew>

It was being interpreted as a Hugo shortcode.

layouts/partials/docs/content_page.html

@@ -1,4 +1,4 @@
-<p><a href="{{ printf "%s#%s" ("docs/editdocs" | relURL) .page.Path | safeURL }}" id="editPageButton">Edit This Page</a></p>
+<p><a href="https://github.com/kubernetes/website/edit/master/content/en/{{ .page.File.Path }}" id="editPageButton" target="_blank">Edit This Page</a></p>
 {{ if not .page.Params.notitle }}
 <h1>{{ .page.Title }}</h1>
 {{ end }}