[SharedTextureMemory] Add documentation of texture creation constraints

These constraints are enforced here [1].

[1] https://source.chromium.org/chromium/chromium/src/+/main:third_party/dawn/src/dawn/native/SharedTextureMemory.cpp;l=159-168?q=SharedTextureMemory.cp&ss=chromium

Change-Id: Ib875f6730637f789ab9ed3fe0c0ccd8609783f9c
Bug: dawn:2152
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/168649
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Colin Blundell <blundell@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
diff --git a/docs/dawn/features/shared_texture_memory.md b/docs/dawn/features/shared_texture_memory.md
index b499859..14293cf 100644
--- a/docs/dawn/features/shared_texture_memory.md
+++ b/docs/dawn/features/shared_texture_memory.md
@@ -43,6 +43,13 @@
 wgpu::Texture texture = memory.CreateTexture(&textureDesc);
 ```
 
+Note: There are restrictions on the configuration that can be requested for
+textures created from SharedTextureMemory objects:
+- they must be single-sampled
+- they must be 2D
+- they must have a single mip level
+- they must have an array layer count of 1
+
 Textures created from shared texture memory are not valid to use inside a queue operation until access to the memory is explicitly started using `BeginAccess`. Access is ended using `EndAccess`. For example:
 
 ```c++