Update readthedocs configuration

.readthedocs.yml

@@ -7,14 +7,21 @@ sphinx:
   configuration: docs/source/conf.py
 
 build:
-    image: latest
+  os: ubuntu-22.04
+  tools:
+    python: "3.8"
 
 python:
-    version: 3.8
-    install:
-      - method: pip
-        path: .
-        extra_requirements:
-           - docs
-      - method: setuptools
-        path: .
+  install:
+    - requirements: requirements.txt
+    - requirements: docs/doc_requirements.txt
+    - method: pip
+      path: .
+      extra_requirements:
+        - docs
+    - method: setuptools
+      path: .
+
+formats:
+  - htmlzip
+  - epub