Improve and modernize docs. (#2882)

* Add proper home landing page.

* Improve landing page considerably.

* Add navbar library name.

* Fix css rules.

* Update getting started images.

* Change favicon to the navbar's logo.

* Tiny change to docs index.

* Add title to home landing page.

* Tweak build overrides faq page.

* Fix FAQ article titles and headers.

* Fix FAQ article titles and headers.

* Replace channel 9 with the official .net course.

docs/toc.yml

@@ -1,11 +1,13 @@
+- name: Home
+  href: index.md
+- name: Documentation
+  href: api/
+  topicUid: API.Docs
 - name: Guides
   href: guides/
   topicUid: Guides.Introduction
 - name: FAQ
   href: faq/
   topicUid: FAQ.Basics.GetStarted
-- name: API Documentation
-  href: api/
-  topicUid: API.Docs
 - name: Changelog
   href: ../CHANGELOG.md