Fix issues building docs.

Author: owo

.readthedocs.yml

@@ -1,10 +1,17 @@
 version: 2
 
+build:
+  os: ubuntu-22.04
+  apt_packages:
+    - cmake
+    - libboost-dev
+  tools:
+    python: "3.7"
+
 sphinx:
   configuration: docs/source/conf.py
 
 python:
-  version: 3.7
   install:
     - requirements: docs/requirements.txt
     - method: pip