doc: clarify child_process.exec inherits cwd

PR-URL: #36809
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Pooja D P <Pooja.D.P@ibm.com>
Reviewed-By: Yash Ladha <yash@yashladha.in>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/child_process.md

@@ -154,7 +154,7 @@ changes:
 * `command` {string} The command to run, with space-separated arguments.
 * `options` {Object}
   * `cwd` {string} Current working directory of the child process.
-    **Default:** `null`.
+    **Default:** `process.cwd()`.
   * `env` {Object} Environment key-value pairs. **Default:** `process.env`.
   * `encoding` {string} **Default:** `'utf8'`
   * `shell` {string} Shell to execute the command with. See