Update Wasm README.md

Closes #55707

GitOrigin-RevId: 3ea1f9d
Change-Id: I83f6ff440257c2de9c57aa92d31f7e09603f5e0e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/366224
Reviewed-by: Kevin Moore <kevmoo@google.com>
Commit-Queue: Michael Thomsen <mit@google.com>

pkg/dart2wasm/README.md

@@ -1,19 +1,14 @@
-# Compiling Dart to WebAssembly
+# Compiling Dart to WebAssembly (internal SDK developer notes)
 
-WebAssembly (commonly abbreviated to Wasm) is a
-_"binary instruction format for a stack-based virtual machine"_.
-Although Wasm was originally designed for running native code on the web,
-Wasm has since evolved into a general technology for running
-compiled code across multiple platforms.
-
-The Dart team is currently investigating support for compiling Dart to Wasm,
-in conjunction with support [in Flutter](https://flutter.dev/wasm).
+**This page contains notes for how to compile to WebAssembly for SDK contributors.
+If you are a Dart developer, using a prebuilt Dart SDK, please refer to the
+[regular documentation](https://dart.dev/web/wasm).**
 
 **Note:** This feature is under active development,
 and is currently considered experimental.
 The tracking issue is [#32894](https://github.com/dart-lang/sdk/issues/32894).
 
-## Running dart2wasm
+## Running dart2wasm as an SDK contributor
 
 You don't need to build the Dart SDK to run dart2wasm, as long as you have a Dart SDK installed and have the [Dart SDK repository checked out](https://github.com/dart-lang/sdk/wiki/Building#getting-the-source). NB: the SDK must be checked out using depot tools and not just cloned from this repo.
 
@@ -23,7 +18,7 @@ To compile a Dart file to Wasm, in a checkout of the Dart SDK repository, run:
 dart --enable-asserts pkg/dart2wasm/bin/dart2wasm.dart <options> <input file>.dart <output file>.wasm
 ```
 
-where *options* include:
+### Compiler options
 
 | Option                                  | Default | Description |
 | --------------------------------------- | ------- | ----------- |