UI documentation fixes

Make the 'learn' section on the index page consistent with the nav bar
tab. Prompt 'views' doc up a bit, and use an image(credit to @ellyjones)
instead of ASCII diagram for better understanding.

Bug: none
Change-Id: Iac2c59e3c28a0f5021bc398ffad80929435a797c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2417072
Reviewed-by: Robert Liao <[email protected]>
Commit-Queue: Robert Liao <[email protected]>
Cr-Commit-Position: refs/heads/master@{#808583}
diff --git a/docs/ui/learn/index.md b/docs/ui/learn/index.md
index 8594fad..bd23aef 100644
--- a/docs/ui/learn/index.md
+++ b/docs/ui/learn/index.md
@@ -6,5 +6,18 @@
 * [Layout](bestpractices/layout.md): How to use Views layout.
 * [Ownership](bestpractices/ownership.md): How to manage Views object lifetimes.
 
-# Architecture Overview
-Coming soon.
+# Chrome UI
+
+* [Views](/docs/ui/views/overview.md)
+* [Product Excellence](/docs/ui/product_excellence/index.md)
+* [UI Devtools](/docs/ui/ui_devtools/index.md)
+
+# Archival Documentation on Chrome UI.
+
+* [Aura](/docs/ui/aura/index.md)
+* [Compositor](/docs/ui/compositor/index.md)
+
+# Processes
+
+* [Frontline Triage Procedures](frontline_triage.md)
+