update readthedocs configuration

Author: Paul Kienzle

.readthedocs.yaml

@@ -16,7 +16,9 @@ build:
   commands:
     - pip install matplotlib sphinx
     - make -j 4 -C doc/sphinx SPHINXOPTS="-W --keep-going" html
-  
+    - mkdir -p $READTHEDOCS_OUTPUT/html
+    - cp -rp doc/sphinx/_build/html/ $READTHEDOCS_OUTPUT/html/
+
 # Build documentation in the "doc/" directory with Sphinx
 #sphinx:
   #configuration: doc/sphinx/conf.py