Trim intro copy and give it a supporting image

The intro was the only slide/page without a graphic. Shortened it to two
sentences and added a matching photo, and dropped the CSS rule that let
Step 1 share a print page with the intro (needed now that the intro has
its own image and deserves a full page like every other section).

README.md

@@ -66,9 +66,9 @@ make partners/<slug>.pdf
 
 ## Notes
 
-- The 4 photos in `images/` were extracted from the original PDF. They're intentionally
-  generic/illustrative (not specific to any one partnership) and don't need to change
-  per customization.
+- The photos in `images/` (4 extracted from the original PDF, plus `intro-reader.jpg`
+  sourced from Pexels) are intentionally generic/illustrative (not specific to any one
+  partnership) and don't need to change per customization.
 - `template.html` renders the cover (title + byline + author photo) from the document's
   YAML front matter — you don't need to hand-write that part in the body of each `.md`
   file, just update the front matter.