bpo-41455: Provide a link to how the third generation is collected in the GC docs (GH-21703)


Co-authored-by: Pablo Galindo <Pablogsal@gmail.com>
(cherry picked from commit 82ca8fada15b121866530f2cdac1b7055be4a244)

Co-authored-by: Yaroslav Pankovych <31005942+P-Alban@users.noreply.github.com>
diff --git a/Doc/library/gc.rst b/Doc/library/gc.rst
index 0c33c86..2d85cd3 100644
--- a/Doc/library/gc.rst
+++ b/Doc/library/gc.rst
@@ -106,9 +106,9 @@
    allocations minus the number of deallocations exceeds *threshold0*, collection
    starts.  Initially only generation ``0`` is examined.  If generation ``0`` has
    been examined more than *threshold1* times since generation ``1`` has been
-   examined, then generation ``1`` is examined as well.  Similarly, *threshold2*
-   controls the number of collections of generation ``1`` before collecting
-   generation ``2``.
+   examined, then generation ``1`` is examined as well.
+   With the third generation, things are a bit more complicated,
+   see `Collecting the oldest generation <https://devguide.python.org/garbage_collector/#collecting-the-oldest-generation>`_ for more information.
 
 
 .. function:: get_count()