update section on error boundary

Author: inventarSarah

docs/platforms/javascript/guides/react/index.mdx

@@ -54,7 +54,7 @@ Sentry supports multiple versions of React Router. To learn how to configure the
 
 ### Initialize the Sentry SDK
 
-To import and initialize Sentry, create a file, for example, `instrument.js`, in your project and add the following code:
+To import and initialize Sentry, create a file in your project's root directory, for example, `instrument.js`, and add the following code:
 
 ```javascript {filename:instrument.js} {"onboardingOptions": {"performance": "3-8, 13-21, 24-30", "session-replay": "22, 33-39"}}
 import { useEffect } from "react";
@@ -142,7 +142,7 @@ root.render();
 
 ### Add Error Boundary Components (React \<19)
 
-Use the [Error Boundary](features/error-boundary/) component to automatically send errors from specific component trees to Sentry and provide a fallback UI:
+Use the [`ErrorBoundary`](features/error-boundary/) component to automatically send errors from specific component trees to Sentry and provide a fallback UI:
 
 ```javascript
 import React from "react";
@@ -153,6 +153,12 @@ import * as Sentry from "@sentry/react";
 </Sentry.ErrorBoundary>;
 ```
 
+<Alert level="info">
+  To capture errors manually with your own error boundary, use the
+  `captureReactException` function as described
+  [here](features/error-boundary/#manually-capturing-errors).
+</Alert>
+
 <OnboardingOption optionId="performance">
 ## Step 4: Set Up React Router