doc: update example of using await in REPL

Lexical scope of `const` is only invalidated when
using top-level `await` in REPL.

Fixes: #45918

Author: deokjinkim

doc/api/repl.md

@@ -234,6 +234,20 @@ undefined
 undefined
 ```
 
+One known limitation of using the `await` keyword in the REPL is that
+it will invalidate the lexical scoping of the `const` keywords.
+
+For example:
+
+```console
+> const m = await Promise.resolve(123)
+undefined
+> m
+123
+> m = await Promise.resolve(234)
+234
+```
+
 [`--no-experimental-repl-await`][] shall disable top-level await in REPL.
 
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