Manually add the docker files to manifest file

Otherwise the *.* glob does not match them

MANIFEST.in

@@ -1,17 +1,20 @@
+# Files in root folder
 include README.rst
 include AUTHORS.txt
 include AGPL.txt
 include CC-BY-SA.txt
 include requirements.txt
 include requirements_devel.txt
 
+# Application folder as well as extras
 recursive-include extras *.*
 recursive-include wger *.*
 recursive-exclude wger *.pyc
 recursive-exclude wger *.swp
 recursive-exclude wger *~
+include extras/docker/*/Dockerfile
 
-# added by check_manifest.py
+# Documentation
 recursive-include docs *.bat
 recursive-include docs *.py
 recursive-include docs *.rst