docs: deliver the user guide as a formatted PDF

The guide now ships as `doc/Rectify_user_guide.pdf` alongside the Markdown
it is rendered from. The PDF is the one to read; the Markdown remains the
source and is authoritative if the two ever disagree.

It is committed rather than built here because rendering it needs a font
store and a headless browser, which no one should have to install in order
to read a guide. The same PDF is downloadable on its own from
https://andykopra.com/Rectify_user_guide.pdf — the macOS disk image holds
the application only.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.gitignore

@@ -44,3 +44,17 @@ notes/
 # Editor backup files
 *~
 *.py~
+
+# ktext build products (the user guide is written in Markdown and rendered
+# through Klammertext).  Intermediates are ignored; the rendered PDF is NOT.
+#
+# doc/Rectify_user_guide.pdf is a build product that is deliberately committed,
+# because it is the documentation users receive and nobody downstream can
+# rebuild it: rendering needs Klammertext, its font store, and a Chromium-based
+# browser.  Shipping the source alone would ship nothing readable.  Rebuild it
+# with `make` in doc/ and commit it alongside the Markdown it came from.
+doc/*.aux
+doc/*.log
+doc/*.out
+doc/*.tex
+doc/Rectify_user_guide/