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.

.github/ISSUE_TEMPLATE.md

@@ -1,4 +1,5 @@
 <!-- Thanks for filing an issue! Before submitting, please fill in the following information. -->
+<!-- See https://kubernetes.io/docs/contribute/start/ for guidance on writing an actionable issue description. -->
 
 <!--Required Information-->
 

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,6 +1,9 @@
 >^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+> Please delete this note before submitting the pull request.
 > For 1.12 Features: set Milestone to 1.12 and Base Branch to release-1.12
+> Help editing and submitting pull requests:  https://deploy-preview-9510--kubernetes-io-master-staging.netlify.com/docs/contribute/start/#submit-a-pull-request.
+> Help choosing which branch to use, see
+> https://kubernetes.io/docs/contribute/start#choose-which-git-branch-to-use.
 >^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 >
-> Please delete this note before submitting the pull request.