Fixed tutorial link in "getting_started.mdx" (#2972)

Summary:
The link was broken, so I updated it, it works now.

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## Motivation

The link didn't work for the tutorial section, so I fixed it

### Have you read the [Contributing Guidelines on pull requests](https://github.com/pytorch/botorch/blob/main/CONTRIBUTING.md#pull-requests)?

Yes

Pull Request resolved: #2972

Test Plan:
(Write your test plan here. If you changed any code, please provide us with clear instructions on how you verified your changes work. Bonus points for screenshots and videos!)

If you click the link, it goes to the page

## Related PRs

(If this PR adds or changes functionality, please take some time to update the docs at https://github.com/pytorch/botorch, and link to your PR here.)

Reviewed By: esantorella

Differential Revision: D80178391

Pulled By: CristianLara

fbshipit-source-id: ddc3b806d60984b99fe05f941e2be33197b59034

Author: SpencerHalle

docs/getting_started.mdx

@@ -88,7 +88,7 @@ Here's a quick run down of the main components of a Bayesian Optimization loop.
 ## Tutorials
 
 Our Jupyter notebook tutorials help you get off the ground with BoTorch.
-View and download them [here](tutorials).
+View and download them [here](tutorials/index.mdx).
 
 
 ## API Reference