docs: rebuild README around the user workflow

tests/ipc-contract.test.mjs

@@ -41,7 +41,7 @@ test("every renderer bridge call is exposed by the preload contract", async () =
     ),
   );
   const exposed = new Set(
-    [...preload.matchAll(/^\s{2}([A-Za-z0-9_]+):/gm)].map((match) => match[1]),
+    [...preload.matchAll(/^\s+([A-Za-z0-9_]+):/gm)].map((match) => match[1]),
   );
   assert.ok(calls.size > 40, "expected the complete renderer bridge surface");
   assert.deepEqual(