Update text/3668-async-closures.md

add the note in one other place

Co-authored-by: Josh Triplett <[email protected]>

text/3668-async-closures.md

@@ -111,6 +111,8 @@ In order for this to work, the `FnMut` trait would need to be ["lending"](https:
 
 # Guide Level Explanation
 
+(**note**: See the [naming blocking concern](#what-do-we-call-the-trait) about `async Fn*` vs `AsyncFn*` syntax. This RFC uses the `async Fn` syntax for trait bounds to avoid duplicating explanations for two different proposed syntaxes, but the syntax remains an open question.)
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 Just as you can write functions which accept closures, you can write functions which accept async closures:
 
 ```rust