gh-39862: adding some pyx modules to the documentation
    
inspired by #35468

only solve this partially.

```
from pathlib import Path
p = Path("src/sage")
data=list(p.rglob("*.pyx"))
resu = []
for a in data:
    proc = subprocess.Popen(["git","grep",str(a.stem),"src/doc/en/refere
nce"],stdout=PIPE, stderr=PIPE)
    x, y = proc.communicate()
    if not x:
        resu.append(a)
```

### 📝 Checklist

- [x] The title is concise and informative.
- [x] I have linked a relevant issue or discussion.
    
URL: #39862
Reported by: Frédéric Chapoton
Reviewer(s): David Coudert

Author: Release Manager

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

@@ -46,9 +46,11 @@ Named associative algebras
    sage/algebras/askey_wilson
    sage/combinat/diagram_algebras
    sage/algebras/clifford_algebra
+   sage/algebras/clifford_algebra_element
    sage/algebras/cluster_algebra
    sage/combinat/descent_algebra
    sage/algebras/down_up_algebra
+   sage/algebras/exterior_algebra_groebner
    fusion_rings
    sage/algebras/hall_algebra
    sage/combinat/posets/incidence_algebras

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

@@ -53,6 +53,7 @@ Individual Categories
    sage/categories/bialgebras
    sage/categories/bialgebras_with_basis
    sage/categories/bimodules
+   sage/categories/chain_complexes
    sage/categories/classical_crystals
    sage/categories/coalgebras
    sage/categories/coalgebras_with_basis
@@ -70,6 +71,7 @@ Individual Categories
    sage/categories/coxeter_groups
    sage/categories/crystals
    sage/categories/cw_complexes
+   sage/categories/dedekind_domains
    sage/categories/discrete_valuation
    sage/categories/distributive_magmas_and_additive_magmas
    sage/categories/division_rings
@@ -79,6 +81,7 @@ Individual Categories
    sage/categories/fields
    sage/categories/filtered_algebras
    sage/categories/filtered_algebras_with_basis
+   sage/categories/filtered_hopf_algebras_with_basis
    sage/categories/filtered_modules
    sage/categories/filtered_modules_with_basis
    sage/categories/finite_complex_reflection_groups
@@ -160,6 +163,7 @@ Individual Categories
    sage/categories/modules_with_basis
    sage/categories/monoid_algebras
    sage/categories/monoids
+   sage/categories/noetherian_rings
    sage/categories/number_fields
    sage/categories/objects
    sage/categories/ore_modules

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

@@ -79,8 +79,10 @@ Libraries of algorithms
    sage/graphs/centrality
    sage/graphs/asteroidal_triples
    sage/graphs/independent_sets
+   sage/graphs/chrompoly
    sage/graphs/cographs
    sage/graphs/comparability
+   sage/graphs/isoperimetric_inequalities
    sage/graphs/line_graph
    sage/graphs/spanning_tree
    sage/graphs/pq_trees
@@ -99,6 +101,7 @@ Libraries of algorithms
    sage/graphs/graph_decompositions/rankwidth
    sage/graphs/graph_decompositions/bandwidth
    sage/graphs/graph_decompositions/cutwidth
+   sage/graphs/graph_decompositions/fast_digraph
    sage/graphs/graph_decompositions/graph_products
    sage/graphs/graph_decompositions/slice_decomposition
    sage/graphs/graph_decompositions/modular_decomposition

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

@@ -74,6 +74,7 @@ Internals
    sage/matroids/lean_matrix
    sage/matroids/matroids_plot_helpers
    sage/matroids/set_system
+   sage/matroids/union_matroid
    sage/matroids/unpickling
 
 .. include:: ../footer.txt

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

@@ -100,6 +100,8 @@ Miscellaneous Modules (to be sorted)
    sage/modular/quatalg/brandt
    sage/modular/cusps_nf
    sage/modular/hypergeometric_motive
+   sage/modular/hypergeometric_misc
    sage/modular/multiple_zeta
+   sage/modular/modform/l_series_gross_zagier_coeffs
 
 .. include:: ../footer.txt

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

@@ -135,5 +135,6 @@ Misc
    sage/modules/tensor_operations
    sage/modules/finite_submodule_iter
    sage/modules/misc
+   sage/modules/numpy_util
 
 .. include:: ../footer.txt

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

@@ -6,6 +6,6 @@ Quaternion Algebras
 
    sage/algebras/quatalg/quaternion_algebra
    sage/algebras/quatalg/quaternion_algebra_element
-
+   sage/algebras/quatalg/quaternion_algebra_cython
 
 .. include:: ../footer.txt

src/sage/algebras/exterior_algebra_groebner.pyx

@@ -438,6 +438,8 @@ cdef class GroebnerStrategy:
         """
         Convert the computed Gröbner basis to a reduced Gröbner basis.
 
+        EXAMPLES::
+
             sage: E.<x,y,z> = ExteriorAlgebra(QQ)
             sage: I = E.ideal([x+y*z])
             sage: I.groebner_basis(reduced=False)

src/sage/graphs/graph_decompositions/fast_digraph.pyx

@@ -90,7 +90,7 @@ cdef class FastDigraph:
 
     def print_adjacency_matrix(self):
         r"""
-        Displays the adjacency matrix of ``self``.
+        Display the adjacency matrix of ``self``.
 
         EXAMPLES::
 

src/sage/matroids/union_matroid.pyx

@@ -1,3 +1,6 @@
+"""
+Union of matroids
+"""
 from sage.matroids.matroid cimport Matroid
 
 cdef class MatroidUnion(Matroid):

src/sage/modular/hypergeometric_misc.pyx

@@ -1,6 +1,7 @@
 """
-Some utility routines for the hypergeometric motives package that benefit
-significantly from Cythonization.
+Utility routines for hypergeometric motives
+
+These are functions that benefit significantly from Cythonization.
 """
 from cpython cimport array
 from cysignals.signals cimport sig_check

src/sage/modular/modform/l_series_gross_zagier.py

@@ -1,3 +1,6 @@
+"""
+Gross-Zagier L-series
+"""
 from sage.rings.integer import Integer
 from sage.structure.sage_object import SageObject
 from sage.lfunctions.dokchitser import Dokchitser

src/sage/modular/modform/l_series_gross_zagier_coeffs.pyx

@@ -1,3 +1,6 @@
+"""
+Utilities for Gross-Zagier L-series
+"""
 from cysignals.memory cimport check_allocarray, check_calloc, sig_free
 from cysignals.signals cimport sig_check, sig_on, sig_off
 
@@ -14,7 +17,7 @@ from libc.string cimport memcpy
 
 cpdef to_series(L, var):
     """
-    Create a power series element out of a list ``L`` in the variable`` var``.
+    Create a power series element out of a list ``L`` in the variable ``var``.
 
     EXAMPLES::
 
@@ -42,7 +45,7 @@ def bqf_theta_series(Q, long bound, var=None):
 
     .. MATH::
 
-        \sum_{(x,y) \in \Z^2} q^{f(x,y)} = \sum_{n=-\infty}^{\infty} r(n)q^n
+        \sum_{(x,y) \in \ZZ^2} q^{f(x,y)} = \sum_{n=-\infty}^{\infty} r(n)q^n
 
     where `r(n)` give the number of way `n` is represented by `f`.