Document api modules and require explicit imports of API submodules

src/ifcopenshell-python/ifcopenshell/api/layer/__init__.py

@@ -16,8 +16,20 @@
 # You should have received a copy of the GNU Lesser General Public License
 # along with IfcOpenShell.  If not, see <http://www.gnu.org/licenses/>.
 
+"""Manage CAD layers
+
+Note that in IFC, elements cannot be assigned to CAD layers. Instead, the
+geometric representation of the element is associated to a layer.
+
+If you want to associated a whole element to a "layer", consider using
+:mod:`ifcopenshell.api.classification`.
+"""
+
+from .. import wrap_usecases
 from .add_layer import add_layer
 from .assign_layer import assign_layer
 from .edit_layer import edit_layer
 from .remove_layer import remove_layer
 from .unassign_layer import unassign_layer
+
+wrap_usecases(__path__, __name__)