Ignore venv and env directories

That way virtual environments will be skipped and not trigger a spate of warnings.

conf.py

@@ -70,7 +70,7 @@
 
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.
-exclude_patterns = ['_build']
+exclude_patterns = ['_build', 'venv*', 'env*']
 
 # The reST default role (used for this markup: `text`) to use for all documents.
 #default_role = None