Use dirhtml builder for Read the Docs (#965)

* Use dirhtml builder for Read the Docs

* Move built docs to expected directory

Author: hugovk

.readthedocs.yml

@@ -14,4 +14,5 @@ build:
     python: "3.10"
 
   commands:
-    - make html BUILDDIR=_readthedocs
+    - make dirhtml BUILDDIR=_readthedocs
+    - mv _readthedocs/dirhtml _readthedocs/html