Fix Dockerfile to build successfully without models directory (#210)

Dockerfile

@@ -12,7 +12,7 @@ COPY haystack /home/user/haystack
 COPY rest_api /home/user/rest_api
 
 # copy saved FARM models
-COPY models /home/user/models
+COPY README.rst models* /home/user/models
 
 # optional : copy sqlite db if needed for testing
 #COPY qa.db /home/user/