fix .readthedocs.yaml, fixes #559 (#560)

Author: ThomasWaldmann

.readthedocs.yaml

@@ -7,6 +7,17 @@ build:
   os: ubuntu-22.04
   tools:
     python: "3.11"
+  apt_packages:
+    - build-essential
+  jobs:
+    pre_install:
+      - pip install -r requirements.txt
+      - make cython
+
+python:
+  install:
+    - method: pip
+      path: .
 
 sphinx:
   configuration: docs/conf.py