Update .readthedocs.yaml

Author: pockerman

.readthedocs.yaml

@@ -21,6 +21,8 @@ build:
       - pip install breathe==4.35.0
       - pip install -U exhale==0.3.7
       - pip install sphinx_rtd_theme==3.0.2
+    build:
+      - python -m sphinx -T -b html -d _build/doctrees -D language=en . $READTHEDOCS_OUTPUT/html 
 
 
 # Build documentation in the "docs/" directory with Sphinx