Document scripts/demos/ in the README architecture overview

It existed since the matplotlib-demo relocation but was never added
to the architecture listing.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

@@ -55,6 +55,12 @@ tracer.py                    Logs traced variables to .mat files (for
                              offline analysis/tuning in MATLAB/Octave,
                              see results.m / results_tc.m).
 
+scripts/demos/               Standalone, eyeballed-plot demos (matplotlib)
+                             exercising components/* in isolation — pid/,
+                             plant/, and a full mash-schedule run in sud/.
+                             Not used at runtime; run directly, e.g.
+                             `python -m scripts.demos.sud.demo_sud`.
+
 sude/                        Mash schedules ("Sud" = brew/wort), each a
                              JSON list of temperature rests ("Rasten")
                              with target temperature, heat rate, and