error was in the extension of the image file (!)

josemiotto · josemiotto · commit 64c525f273d0 · 2020-05-30T10:38:28.000+02:00
diff --git a/docs/source/index.rst b/docs/source/index.rst
@@ -12,7 +12,7 @@ Welcome to pylevy's documentation!
 
    levy
 
-.. image:: _static/levy_distributions.pdf
+.. image:: _static/levy_distributions.png
    :width: 600
 
 Indices and tables
