[docs] Initial skeleton for the UX Style Guide.

This CL adds an initial skeleton for the UX Style Guide and also
merges the

1. go/chrome-devtools/ux-writing and
2. go/chrome-devtools/ui-glossary

documentation sets into this already, as well as moving and slightly
adjusting the Material 3 styling documentation.

Bug: 354102605
Change-Id: Ida1e5e47038fac421e665eac9785bdc1fe04d6de
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/5725533
Commit-Queue: Kim-Anh Tran <[email protected]>
Commit-Queue: Benedikt Meurer <[email protected]>
Reviewed-by: Kim-Anh Tran <[email protected]>
Auto-Submit: Benedikt Meurer <[email protected]>
diff --git a/docs/styleguide/ux/README.md b/docs/styleguide/ux/README.md
new file mode 100644
index 0000000..b3a4004
--- /dev/null
+++ b/docs/styleguide/ux/README.md
@@ -0,0 +1,13 @@
+# Chromium DevTools UX Style Guide
+
+These guidelines cover the best practices for extending Chromium DevTools'
+user interface.
+
+## Table of contents
+
+1. [How to organize UI](organizing.md)
+1. [How to style UI](styling.md)
+1. [How to write UI text](writing.md)
+1. [Glossary](glossary.md)
+
+Back to the [Chromium DevTools Documentation](../../README.md).