DOC: Extend explanation on how to build the documentation

src/doc/README_SETUP.md

@@ -13,7 +13,10 @@ see INSTALL.md
 We use sphinx to create the documentation. Docstrings in the code should comply
 with the Googly style (see link below).
 
-Build documentation in `src/doc` with `make html`.
+Build documentation in `src/doc` with `make doc`. Note that for the
+automatic generation of the complete API documentation, it is
+necessary to first install this library with all its optional
+dependencies, i.e., `pip install .[h5-crawler,spss]`.
 
 ### Requirements ###