Documentation: add Sorting section to kernel-api

Add sort() and list_sort() to the kernel API documentation in a
new "Sorting" section.
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/core-api/kernel-api.rst

@@ -139,6 +139,15 @@ Division Functions
 .. kernel-doc:: lib/gcd.c
    :export:
 
+Sorting
+-------
+
+.. kernel-doc:: lib/sort.c
+   :export:
+
+.. kernel-doc:: lib/list_sort.c
+   :export:
+
 Memory Management in Linux
 ==========================