diff --git a/build/fig/cs_sph.asy b/build/fig/cs_sph.asy
new file mode 100644
index 0000000..e362704
--- /dev/null
+++ b/build/fig/cs_sph.asy
@@ -0,0 +1,13 @@
+settings.outformat="png";
+settings.render=16;
+
+import three;
+
+size(5cm);
+
+draw(O -- 1.2X, arrow=Arrow3(emissive(black)));
+draw(O -- 1.2Y, arrow=Arrow3(emissive(black)));
+draw(O -- 1.2Z, arrow=Arrow3(emissive(black)));
+
+draw(arc(c=O, X, X + 2Y));
+draw(arc(c=O, Z, 0.5*X + Y + 0.8*Z));
diff --git a/build/fig/cs_sph.png b/build/fig/cs_sph.png
new file mode 100644
index 0000000..35cbe4b
Binary files /dev/null and b/build/fig/cs_sph.png differ
diff --git a/readme.org b/readme.org
index 58217f2..b529883 100644
--- a/readme.org
+++ b/readme.org
@@ -4,8 +4,7 @@
 * Pre-Quantum Electrodynamics lecture notes (html export)
 
 In this repo, you will find
-`J.-S. Caux <https://jscaux.org>`_'s
-`Pre-Quantum Electrodynamics <https://jscaux.org/ln/pqed>`_
+[[https://jscaux.org][J.-S. Caux]]'s [[https://jscaux.org/ln/pqed][Pre-Quantum Electrodynamics]]
 online lecture notes (exported to html).
 
 ** Pulling the notes to your local machine
@@ -34,6 +33,12 @@ Pretty easy: just open the =index.org= page (or any other
 =.html= page in the repo) in your browser.
 
 
+** Providing feedback
+
+You can either [[mailto:prof@jscaux.org][email me]] or [[https://jscaux.org/git/jscaux/pqed_html/issues][create an issue in this repo]] .
+Your feedback is most welcome.
+
+
 ** Learning git
 
 `git <https://git-scm.com/>`_ is one of those applications which