repl: document top level await limitation with const/let

Fixes: #17669
Signed-off-by: James M Snell <jasnell@gmail.com>

PR-URL: #38449
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>

Author: jasnell

doc/api/repl.md

@@ -233,6 +233,23 @@ undefined
 undefined
 ```
 
+One known limitation of using the `await` keyword in the REPL is that
+it will invalidate the lexical scoping of the `const` and `let`
+keywords.
+
+For example:
+
+```console
+> const m = await Promise.resolve(123)
+undefined
+> m
+123
+> const m = await Promise.resolve(234)
+undefined
+> m
+234
+```
+
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