Note that the polyfill and other docs are no longer being updated

Closes #32

Also further notes that the proposal cannot be high-fidelity polyfilled
because the "fail fast synchronously" semantics cannot be correctly
polyfilled on top of Atomics.wait.

PROPOSAL.md

@@ -93,7 +93,10 @@ See the [draft spec text](https://tc39.github.io/proposal-atomics-wait-async/).
 
 ## Polyfills
 
-(NOTE: The current polyfill is out of date.)
+(NOTE: The current polyfill is out of date and no longer maintained. Further,
+the proposal cannot be polyfilled in a high-fidelity manner using
+`Atomics.wait`, because there is no atomics way to synchronously handle the
+`"not-equal"` case.)
 
 A simple polyfill is possible.
 

README.md

@@ -5,6 +5,11 @@ for use in agents that are not allowed to block.
 
 Champions: Shu-yu Guo (Google) and Lars T Hansen (Mozilla).
 
+## Historical documents
+
+Warning: The following documents are no longer being updated and are of
+historical interest only.
+
 See [PROPOSAL.md](PROPOSAL.md) for the evolving proposal text,
 [polyfill.js](polyfill.js) for a simple polyfill implementation, and
 [example.html](example.html) for some examples and test cases; this