bpo-26589: Add http status code 451 (GH-15413)

diff --git a/Doc/library/http.rst b/Doc/library/http.rst
index 88d62cc..8df1457 100644
--- a/Doc/library/http.rst
+++ b/Doc/library/http.rst
@@ -106,6 +106,7 @@
 ``428`` ``PRECONDITION_REQUIRED``           Additional HTTP Status Codes :rfc:`6585`
 ``429`` ``TOO_MANY_REQUESTS``               Additional HTTP Status Codes :rfc:`6585`
 ``431`` ``REQUEST_HEADER_FIELDS_TOO_LARGE`` Additional HTTP Status Codes :rfc:`6585`
+``451`` ``UNAVAILABLE_FOR_LEGAL_REASONS``   An HTTP Status Code to Report Legal Obstacles :rfc:`7725`
 ``500`` ``INTERNAL_SERVER_ERROR``           HTTP/1.1 :rfc:`7231`, Section 6.6.1
 ``501`` ``NOT_IMPLEMENTED``                 HTTP/1.1 :rfc:`7231`, Section 6.6.2
 ``502`` ``BAD_GATEWAY``                     HTTP/1.1 :rfc:`7231`, Section 6.6.3
@@ -126,3 +127,6 @@
 
 .. versionchanged:: 3.7
    Added ``421 MISDIRECTED_REQUEST`` status code.
+
+.. versionadded:: 3.8
+   Added ``451 UNAVAILABLE_FOR_LEGAL_REASONS`` status code.