Correct the desktop app's published-wheel version caveat

The README implied some published wheels carry kolibri/_version.py. None
do -- setuptools-scm landed after the latest release -- so `make get-whl`
against any release URL currently fails the version read, including the
v0.18.0 example the README hands the reader. Say so where they'll hit it.

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

Author: rtibblesbot

platforms/desktop-app/README.md

@@ -68,11 +68,11 @@ Builds Kolibri from the monorepo workspace and stages it into `whl/`, so the app
   ```
 
 - **Or Fetch and Prepare a Published Kolibri Wheel:**
-You'll need the URL of the Kolibri `.whl` file for the version you intend to package. You can find release URLs on the [Kolibri GitHub Releases page](https://github.com/learningequality/kolibri/releases). Wheels published before Kolibri adopted setuptools-scm do not contain the `kolibri/_version.py` the build reads for the app version — use `make stage-workspace-whl` for those.
+You'll need the URL of the Kolibri `.whl` you intend to package — see the [Kolibri GitHub Releases page](https://github.com/learningequality/kolibri/releases). The build reads the app version from `kolibri/_version.py`, which no wheel published so far contains, so this path needs a wheel built after Kolibri adopted setuptools-scm; otherwise use `stage-workspace-whl`.
   ```
   make get-whl whl="<URL_TO_KOLIBRI_WHL_FILE>"
   ```
-  **Example:**
+  **Example** (a v0.18.0 wheel predates `_version.py`, so it fails the version read):
   ```
   make get-whl whl="https://github.com/learningequality/kolibri/releases/download/v0.18.0/kolibri-0.18.0-py2.py3-none-any.whl"
   ```