Docs: note the Vulkan layer needs vk_layer.h (not in Vulkan-Headers)

The opt-in implicit-layer piece requires the loader/layer interface header
vk_layer.h, which Vulkan-Headers doesn't ship (it's in Vulkan-Loader / the SDK)
-- so it needs a new submodule or hand-declared link structs, confirming it's a
separate, higher-risk component rather than a quick add.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -169,8 +169,11 @@ Conventions for every milestone below:
     per-user (HKCU, no admin) and scoped to the target image, with an **opt-in** "Set up Vulkan
     layer" Injection-panel checkbox that registers/unregisters it (self-deactivating for non-target
     apps so a stale entry after a host crash is harmless). This is a separate component from the
-    inline-hook capture (layer-chain dispatch + manifest/registry + the checkbox + IPC handshake);
-    until it lands, the banner directs immediate-init Vulkan games to WGC.
+    inline-hook capture (layer-chain dispatch + manifest/registry + the checkbox + IPC handshake),
+    and it needs the loader/layer interface header `vk_layer.h` — which is **not** in
+    `Vulkan-Headers` (it lives in `Vulkan-Loader` / the SDK), so it requires either a new submodule
+    or hand-declared `VkLayer*CreateInfo` link structs. Until it lands, the banner directs
+    immediate-init Vulkan games to WGC (which mirrors them fine, just at higher latency).
 
   Each of 1–3 is its own commit; test the early/layer path against the mock (decode frames) and
   the too-late path (assert the status + banner fire).