docs: ingest how-to says a PDF header carries the outline and the text its colour markings and image-page CHECK (#225 close)

Files changed:
- docs/how-to/ingest-a-source.md

Co-Authored-By: Claude Code <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SnAJ7Z3CpVD3PRbN73QtU2

docs/how-to/ingest-a-source.md

@@ -45,7 +45,12 @@ pick a directory:
   folder is accepted whole; the agent runs this itself when it meets such a file. An Excel file's
   sheets land beside the text as tab-separated files, with their formulas listed apart. A ZIP is
   unpacked into a folder instead, and a mail's attachments land beside it. A scanned PDF has no
-  text to derive - the tool warns, and there is no OCR.
+  text to derive - the tool warns, and there is no OCR. A PDF with an outline gets it in the
+  header of the text, each entry with its page and the line where that page starts; text over a
+  coloured background, in another colour than the running text, or struck through is marked in
+  the text (`<mark data-farbe="gelb">`, `*…*`, `~~…~~`) with a legend in the header, and what a
+  colour means is for the reader to take from the document itself. Pages with pictures are
+  named in a `CHECK` line, because the pictures are not in the text.
 - **A page behind a paywall or a login** is saved from your browser into `incoming/`, HTML only. The
   agent derives the same text from that file with `raw fetch --html`. For a website you read often,
   sign in once instead and let the wiki fetch it with your session: