bpo-37160: Thread native ID NetBSD support (GH-13835)

(cherry picked from commit 5287022eeeb3c017d49fc8580b52e18377bf23f3)

Co-authored-by: David Carlier <dcarlier@afilias.info>
diff --git a/Doc/library/threading.rst b/Doc/library/threading.rst
index 7fb9ac9..b4f4814 100644
--- a/Doc/library/threading.rst
+++ b/Doc/library/threading.rst
@@ -82,7 +82,7 @@
    Its value may be used to uniquely identify this particular thread system-wide
    (until the thread terminates, after which the value may be recycled by the OS).
 
-   .. availability:: Windows, FreeBSD, Linux, macOS, OpenBSD.
+   .. availability:: Windows, FreeBSD, Linux, macOS, OpenBSD, NetBSD.
 
    .. versionadded:: 3.8