Fix docs typo, missing .to_string() (#768)

Compiler was complaining about this. Apparently we need .into() or .to_string(). Feel free to change this to whatever is preferred.

In a previous Sycamore version, was this not required?

docs/next/introduction/your-first-app.md

@@ -275,7 +275,7 @@ Sycamore!".
 
 ```rust
 view! {
-    Hello(name="Sycamore")
+    Hello(name="Sycamore".into())
 }
 ```