fix doc build

Signed-off-by: Morris Jobke <hey@morrisjobke.de>

user_manual/conf.py

@@ -10,6 +10,7 @@
 #
 # All configuration values have a default; values that are commented out
 # serve to show the default.
+import os, inspect
 
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the