docs: JupyterLite troubleshooting section, linked from the README (#134)

* docs: troubleshooting note for Jupyter lite failing to start

A browser holding files from an earlier deploy of the Jupyter lite site
shows many 'Plugin failed to activate / Invalid response: 404' errors
and a broken UI.  Document the fixes: private window, clearing site
data (Safari, Chrome/Edge, Firefox), hard reload, or another browser.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

* docs: make the JupyterLite troubleshooting a section and link it from the README

An admonition buried in the docs would not be found.  Make it a
'Troubleshooting JupyterLite' subsection (so it has a stable anchor) and
link it in small text under the Try it Now badges in the README.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

* docs: add an introductory sentence to the JupyterLite troubleshooting section

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 5.5 <noreply@anthropic.com>

Author: petercorke

README.md

@@ -10,6 +10,8 @@
 [![JupyterLite](https://img.shields.io/badge/Try_it_Now-JupyterLite-orange?style=for-the-badge&logo=jupyter)](https://petercorke.github.io/machinevision-toolbox-python/lite/lab?path=index.ipynb)
   [![PyPI version](https://img.shields.io/pypi/v/machinevision-toolbox-python?style=for-the-badge&color=blue)](https://pypi.org/project/machinevision-toolbox-python/)
   [![Documentation](https://img.shields.io/badge/Docs-View_Online-blue?style=for-the-badge)](https://petercorke.github.io/machinevision-toolbox-python/)
+  <br>
+  <sub><a href="https://petercorke.github.io/machinevision-toolbox-python/jupyter-notebooks.html#troubleshooting-jupyterlite">Troubleshooting JupyterLite</a></sub>
 
   <p>
     <a href="https://github.com/petercorke/machinevision-toolbox-python">GitHub</a> •

docs/source/jupyter-notebooks.rst

@@ -89,10 +89,35 @@ installing anything on your local machine.  To use it, just click the "Launch in
 Lite" button at the top of each notebook page, and it will open the notebook in a new
 browser tab running Jupyter lite.
 
+Troubleshooting JupyterLite
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+JupyterLite is a powerful capability, running a full Python environment inside your
+browser, but it can sometimes get tripped up by what the browser has stored from
+an earlier visit.
+
+If the page loads but the JupyterLab interface is broken, or the console shows many
+``Plugin '...' failed to activate`` / ``Invalid response: 404`` errors, your browser is
+most likely holding files from an earlier version of the site.  Any one of these fixes
+it, quickest first:
+
+* Open the link in a **private / incognito window**, which starts with no stored site data.
+* **Clear the site's data** for ``petercorke.github.io`` and reload.  In Safari this is
+  *Settings* |rarr| *Privacy* |rarr| *Manage Website Data*; in Chrome and Edge it is the
+  icon at the left of the address bar |rarr| *Site settings* |rarr| *Clear data*; in
+  Firefox it is the padlock |rarr| *Clear cookies and site data*.
+* Do a **hard reload** (Shift-click the reload button, or Ctrl/Cmd-Shift-R).
+* Try another browser, or use Colab or a local install instead.
+
+Your own notebooks in Jupyter lite are stored in the same browser data, so clearing the site's data
+deletes them.  Download any notebooks you want to keep first.
+
 
 In the cloud using Google Colab
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
+.. |rarr| unicode:: U+2192
+
 .. |colab_image| image:: https://colab.research.google.com/img/colab_favicon_256px.png
    :height: 30px
    :alt: Open In Colab