Try parallel example generation

With value of 2

Author: PProfizi

doc/source/conf.py

@@ -206,6 +206,7 @@ def reset_servers(gallery_conf, fname, when):
     #                         "set_plot_theme('document')"),
     "reset_modules_order": 'both',
     "reset_modules": (reset_servers,),
+    "parallel": 2,
 }