docs: fix typos in API Reference documentation (#1015)

* docs: fix incorrect caption for add_view code sample

Changed "Using the `@app.view` decorator" to "Using the `app.add_view` method" to more accurately describe the code sample.

* docs: fix logic error in rust code sample

Fix the `square` function's logic to square the number instead of cubing it.

docs_src/src/pages/documentation/api_reference/using_rust_directly.mdx

@@ -44,7 +44,7 @@ The first thing you need to is to create a Rust file. Let's call it `hello_world
 
       #[pyfunction]
       fn square(n: i32) -> i32 {
-          n * n * n
+          n * n
           // this is another comment
       }
 

docs_src/src/pages/documentation/api_reference/views.mdx

@@ -84,7 +84,7 @@ You can serve views in two ways:
 
 <Row>
   <Col>
-  Using an `@app.view` decorator.
+  Using the `app.add_view` method.
   </Col>
   <Col sticky>
     <CodeGroup title="Request" tag="GET" label="/hello_world">