Update the comment at the top of wasi/api.h.

Author: sunfishcode

libc-bottom-half/headers/public/wasi/api.h

@@ -1,13 +1,9 @@
 /**
- * THIS FILE IS AUTO-GENERATED from the following files:
- *   wasi_snapshot_preview1.witx
- *
- * To regenerate this file execute:
- *
- *     cargo run --manifest-path tools/wasi-headers/Cargo.toml generate-libc
- *
- * Modifications to this file will cause CI to fail, the code generator tool
- * must be modified to change this file.
+ * <wasi/api.h>. This file contains declarations describing the WASI ABI
+ * as of "snapshot preview1". It was originally auto-generated from
+ * wasi_snapshot_preview1.witx, however WASI is in the process of
+ * transitioning to a new IDL and header file generator, and this file
+ * is temporarily being manually maintained.
  *
  * @file
  * This file describes the [WASI] interface, consisting of functions, types,