[doc] add missing row about sphinx documentation in README.md

README.md

@@ -162,6 +162,7 @@ cd docs && sphinx-quickstart --project SamGIS --release 1.0.0 --language python
 
 # update docs folder (from project root)
 sphinx-apidoc -f -o docs samgis
+sphinx-apidoc -f -o docs samgis_core
 ```
 
 Then it's possible to generate the HTML pages