doc: mark process.hrtime() as legacy

PR-URL: #38371
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Bryan English <bryan@bryanenglish.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>

Author: aduh95

doc/api/process.md

@@ -1415,6 +1415,8 @@ Indicates whether a callback has been set using
 added: v0.7.6
 -->
 
+> Stability: 3 - Legacy. Use [`process.hrtime.bigint()`][] instead.
+
 * `time` {integer[]} The result of a previous call to `process.hrtime()`
 * Returns: {integer[]}