Flatten marketing paths ahead of wiring up the websites

Drop the redundant documentation/marketing/ nesting inherited from the
plugin repos, so files sit at marketing/<plugin>/<page>.md. These paths
become raw URLs pasted into Elementor pages and ACF fields, so they are
much cheaper to change now than once sites reference them.

Fixes the four cross-plugin links for their new depth, and corrects the
README, which still pointed at the abandoned per-repo documentation/
folders instead of this repo.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

marketing/dotjuice-pagespeed/cdn.md

@@ -0,0 +1,17 @@
+# CDN Integration
+
+Serve your optimised stylesheets and scripts from a CDN hostname, with a single URL change.
+
+## The problem it solves
+
+If you already use a content delivery network to serve assets closer to your visitors geographically, your CSS and JavaScript still need to point at that CDN's hostname rather than your own server for the benefit to apply.
+
+## How it helps
+
+Dotjuice Pagespeed rewrites the URLs of your stylesheets and scripts to point at your CDN hostname automatically, once you tell it what that hostname is — no manual find-and-replace across your theme or plugins required.
+
+## The result
+
+Your optimised CSS and JS served from your CDN with one setting, instead of a manual hunt through every place a stylesheet or script URL is generated.
+
+*Note: this rewrites stylesheet and script URLs specifically. If you're looking to move your entire media library — images, uploaded documents, and so on — onto a CDN, that typically requires a dedicated media-CDN plugin or your CDN provider's own WordPress integration alongside this feature.*