doc: clarify --pending-deprecation effects on Buffer() usage

Refs: #29725 (comment)

PR-URL: #29769
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

doc/api/deprecations.md

@@ -154,9 +154,10 @@ objects:
 * [`Buffer.from(string[, encoding])`][from_string_encoding] - Create a `Buffer`
   that copies `string`.
 
-As of v10.0.0, a deprecation warning is printed at runtime when
-`--pending-deprecation` is used or when the calling code is
-outside `node_modules` in order to better target developers, rather than users.
+Without `--pending-deprecation`, runtime warnings occur only for code not in
+`node_modules`. This means there will not be deprecation warnings for
+`Buffer()` usage in dependencies. With `--pending-deprecation`, a runtime
+warning results no matter where the `Buffer()` usage occurs.
 
 <a id="DEP0006"></a>
 ### DEP0006: child\_process options.customFds