Fix incorrect method name in renderInto docs example

The code example for renderInto was calling renderWhenReady instead.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: captbaritone

packages/webamp-docs/docs/06_API/03_instance-methods.md

@@ -243,7 +243,7 @@ A promise is returned which will resolve after the render is complete.
 
 ```ts
 const container = document.getElementById("webamp-container");
-webamp.renderWhenReady(container).then(() => {
+webamp.renderInto(container).then(() => {
   console.log("rendered webamp!");
 });
 ```