Be honest that Linux and macOS are untested

The setup section and platform notes claimed all three OSes work; the
Linux and macOS statements come from a dependency/code audit only -
nobody has run the plugin there. Say so and ask for reports.

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

README.md

@@ -30,9 +30,12 @@ SWIG API. Requires KiCad **10.0.1+**.
 
 ## Setup (one-time)
 
-The plugin runs on **Windows, Linux and macOS** — KiCad builds it a
-private Python venv from `requirements.txt` on every platform, from
-pre-built wheels only (no compiler needed). Steps 1–4 are the same
+The plugin is developed and tested on **Windows**. **Linux and macOS
+are expected to work but are untested so far** — the code and the
+dependency stack have been audited for all three OSes (KiCad builds
+the plugin a private Python venv from `requirements.txt` on every
+platform, from pre-built wheels only, no compiler needed), but nobody
+has run the plugin there yet. Reports welcome! Steps 1–4 are the same
 everywhere; OS specifics are spelled out per step and in *Platform
 notes* below.
 
@@ -72,20 +75,23 @@ notes* below.
 
 ### Platform notes
 
-- **Windows** is the development and test platform. KiCad's bundled
-  Python is 3.13, so the venv gets the current dependency stack.
-- **macOS** (12+, KiCad's own minimum; Intel and Apple Silicon —
-  the dmg is universal): KiCad's bundled Python is **3.9**, so pip
-  resolves an older but fully functional stack (numpy 2.0,
-  scipy 1.13, matplotlib 3.9, PySide6 6.9/6.10). The plugin code is
-  kept 3.9-compatible. Plot and dialog windows may open **behind**
+- **Windows** is the development and test platform — everything in
+  this README was exercised here. KiCad's bundled Python is 3.13, so
+  the venv gets the current dependency stack.
+- **macOS** — **untested** (audited only: dependency wheels, paths and
+  Python-version compatibility were checked, the plugin was never run
+  on a Mac). Requires macOS 12+ (KiCad's own minimum; Intel and Apple
+  Silicon — the dmg is universal). KiCad's bundled Python is **3.9**,
+  so pip resolves an older stack (numpy 2.0, scipy 1.13,
+  matplotlib 3.9, PySide6 6.9/6.10) that the plugin code is kept
+  compatible with. Expect plot and dialog windows to open **behind**
   the KiCad window (they are raised best-effort) — check the Dock if
   nothing seems to appear after a solve.
-- **Linux**: the venv uses the system Python (3.9+), so the stack
-  matches your distribution. On **ARM64 (aarch64)** there are no
-  pyamg wheels — `requirements.txt` skips pyamg there and the solver
-  falls back to Jacobi-CG: same results, noticeably slower on large
-  grids.
+- **Linux** — **untested** (audited only, same caveat). The venv uses
+  the system Python (3.9+), so the stack matches your distribution.
+  On **ARM64 (aarch64)** there are no pyamg wheels —
+  `requirements.txt` skips pyamg there and the solver falls back to
+  Jacobi-CG: same results, noticeably slower on large grids.
 
 ## Usage