Add missing docs library

.github/workflows/docs.yml

@@ -26,7 +26,7 @@ jobs:
         with:
           python-version: 3.9
       - name: "Install packages for docs building"
-        run: pip install mkdocs-material mkdocs-autorefs 'mkdocstrings[python]'
+        run: pip install mkdocs-material mkdocs-autorefs 'mkdocstrings[python]' docstring_parser
       - name: "Install PySR"
         run: pip install -e .
       - name: "Build API docs"