python: improve docs of gl.Mesh primitive setting.

doc/python/magnum.gl.rst

@@ -50,3 +50,10 @@
     into the mesh or referenced externally (with the user being responsible for
     its lifetime), the `gl.Mesh` object keeps references to all buffers added
     to it.
+
+.. py:property:: magnum.gl.Mesh.primitive
+
+    While querying this property will always give back a `gl.MeshPrimitive`,
+    this property can be set using either `magnum.MeshPrimitive` or
+    `gl.MeshPrimitive`, similarly to how the overloaded
+    :dox:`GL::Mesh::setPrimitive()` works.

src/python/magnum/gl.cpp

@@ -608,7 +608,7 @@ void gl(py::module& m) {
 
     py::class_<GL::Mesh, GL::PyMeshHolder<GL::Mesh>>{m, "Mesh", "Mesh"}
         .def(py::init<GL::MeshPrimitive>(), "Constructor", py::arg("primitive") = GL::MeshPrimitive::Triangles)
-        .def(py::init<MeshPrimitive>(), "Constructor")
+        .def(py::init<MeshPrimitive>(), "Constructor", py::arg("primitive"))
         .def_property_readonly("id", &GL::Mesh::id, "OpenGL vertex array ID")
         .def_property("primitive", &GL::Mesh::primitive,
             [](GL::Mesh& self, py::object primitive) {