n-api: document nextTick timing in callbacks

PR-URL: #33804
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Gabriel Schulhof <gabriel.schulhof@intel.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

doc/api/n-api.md

@@ -4755,6 +4755,9 @@ is sufficient and appropriate. Use of the `napi_make_callback` function
 may be required when implementing custom async behavior that does not use
 `napi_create_async_work`.
 
+Any `process.nextTick`s or Promises scheduled on the microtask queue by
+JavaScript during the callback are ran before returning back to C/C++.
+
 ### napi_open_callback_scope
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