DOC: set nbshpinx_execute to auto

Note: the goal of this change is to avoid computing the
examples twice due to pdf generation

doc/source/conf.py

@@ -408,7 +408,7 @@ def setup(app):
 pygments_style = "sphinx"
 
 # Execute notebooks before conversion
-nbsphinx_execute = "always"
+nbsphinx_execute = "auto"
 
 # Allow errors to help debug.
 nbsphinx_allow_errors = False