Use the new syntaces for GitHub Flavoured Markdown (#420)

See https://github.com/orgs/community/discussions/16925

README.md

diff --git a/README.md b/README.md
index 6eaa5ec..1f0d91d 100644
--- a/README.md
+++ b/README.md
@@ -100,7 +100,7 @@
 cargo run_wasm -p with_winit --bin with_winit_bin
 ```
 
-> **Warning**  
+> [!WARNING]  
 > The web is not currently a primary target for vello, and WebGPU implementations are incomplete, so you might run into issues running this example.
 
 ### Android
@@ -111,7 +111,7 @@
 cargo apk run -p with_winit
 ```
 
-> **Note**  
+> [!TIP]  
 > cargo apk doesn't support running in release mode without configuration. 
 > See [their crates page docs](https://crates.io/crates/cargo-apk) (around `package.metadata.android.signing.<profile>`).
 >