doc: document HPE_HEADER_OVERFLOW error

PR-URL: #23963
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>

doc/api/errors.md

@@ -1843,6 +1843,14 @@ unknown file extension.
 
 Creation of a [`zlib`][] object failed due to incorrect configuration.
 
+<a id="HPE_HEADER_OVERFLOW"></a>
+### HPE_HEADER_OVERFLOW
+
+Too much HTTP header data was received. In order to protect against malicious or
+malconfigured clients, if more than 80KB of HTTP header data is received then
+HTTP parsing will abort without a request or response object being created, and
+an `Error` with this code will be emitted.
+
 <a id="MODULE_NOT_FOUND"></a>
 ### MODULE_NOT_FOUND