Add note about to the README about 2022.12 being the only supported version

Author: asmeurer

Diff for: README.md

@@ -15,6 +15,10 @@ libraries. Consuming library code should use the
 support the array API. Rather, it is intended to be used in the test suites of
 consuming libraries to test their array API usage.
 
+array-api-strict currently supports the 2022.12 version of the standard.
+2023.12 support is planned and is tracked by [this
+issue](https://github.com/data-apis/array-api-strict/issues/25).
+
 ## Install
 
 `array-api-strict` is available on both