sagemathgh-39414: Fix documentation of integral_points

    
Fixes sagemath#39395

Check https://doc-pr-39414--
sagemath.netlify.app/html/en/reference/discrete_geometry/ and
https://doc-pr-39414--sagemath.netlify.app/html/en/reference/discrete_ge
ometry/sage/geometry/integral_points_generic_dense to confirm the issue
is fixed.

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preview.

### ⌛ Dependencies

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URL: sagemath#39414
Reported by: user202729
Reviewer(s):

src/doc/en/reference/discrete_geometry/index.rst

@@ -157,7 +157,11 @@ Helper functions
 
    sage/geometry/fan_isomorphism
    sage/geometry/hasse_diagram
-   sage/geometry/integral_points
+   sage/geometry/integral_points_generic_dense
    sage/geometry/hyperplane_arrangement/check_freeness
 
+..
+   The integral_points_generic_dense entry above should be sage/geometry/integral_points
+   but Sphinx does not handle the Python file containing only import very well
+
 .. include:: ../footer.txt

src/sage/geometry/integral_points_generic_dense.pyx

@@ -1,4 +1,13 @@
 # cython: wraparound=False, boundscheck=False
+r"""
+Cython helper methods to compute integral points in polyhedra
+
+Note that while the URL of this documentation page ends with
+``integral_points_generic_dense``, this is merely to allow Sphinx to generate
+the documentation automatically. Imports should be from
+:mod:`sage.geometry.integral_points`, as can be seen in the examples below.
+Furthermore, not all functions are exported to the public interface.
+"""
 
 from sage.modules.vector_integer_dense cimport Vector_integer_dense as VectorClass
 from sage.matrix.matrix_dense cimport Matrix_dense as MatrixClass