add instructions to run notebooks locally (#107)

example.html

@@ -4,6 +4,29 @@
 ---
 
 Clicking on the example will open a static version of the example, powered by <a href="https://nbviewer.jupyter.org/">nbviewer</a>.
+To interact with a "live" version, it is possible from there to download the notebook and run it locally:
+<ul>
+  <li>open the context menu (via right-click on Linux and Windows, or ctrl-click on macOS)
+    on the download icon of the notebook (in the upper right corner), which will allow
+    you to save the notebook file (say <code>Singular.ipynb</code>) in a directory of your choice
+    (say <code>~/Documents</code>);</li>
+  <li>make sure that you have the <code>Oscar</code> package installed
+    (cf. the <a href="{{ site.baseurl }}/install">installation page</a>);
+    in some cases, you migth have to also install explicitly one of its subpackages, for
+    example <code>Singular</code> (this is accomplished by running
+    <code>using Pkg; Pkg.add("Singular")</code>) in a Julia REPL;</li>
+  <li>install <code>IJulia</code> if it is not already installed (typically by running
+    <code>using Pkg; Pkg.add("IJulia")</code> at the Julia REPL, cf.
+    <a href="https://github.com/JuliaLang/IJulia.jl#Installation">installation instructions</a>),
+    and launch it (typically by running <code>using IJulia; notebook()</code>);</li>
+  <li> you should by now have landed on
+    a page in your web browser, with "jupyter" written in the upper left corner;
+    below is a file explorer: open the notebook file (e.g. browse to
+    <code>~/Documents</code> and click on <code>Singular.ipynb</code>);
+    you might see a pop-up with the message "Kernel not found", in which case
+    just select the Jupyter kernel you installed (e.g. "Julia 1.4.1") in the drop-down menu.
+</ul>
+
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 Clicking on the launch binder button will open an interactive version of