Fix broken link for shape example (#3046)

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### Change Type

- [ ] `patch` — Bug fix
- [ ] `minor` — New feature
- [ ] `major` — Breaking change
- [ ] `dependencies` — Changes to package dependencies[^1]
- [x] `documentation` — Changes to the documentation only[^2]
- [ ] `tests` — Changes to any test code only[^2]
- [ ] `internal` — Any other changes that don't affect the published
package[^2]
- [ ] I don't know

[^1]: publishes a `patch` release, for devDependencies use `internal`
[^2]: will not publish a new version

### Test Plan

1. Add a step-by-step description of how to test your PR here.
2.

- [ ] Unit Tests
- [ ] End to end tests

### Release Notes

- Fix a link that was pointing to a 404 on GitHub

apps/docs/content/docs/shapes.mdx

@@ -89,7 +89,7 @@ While tldraw's shapes themselves are simple JSON objects, we use [ShapeUtil](?)
 
 You can create your own custom shapes. In the examples below, we will create a custom "card" shape. It'll be a simple rectangle with some text inside.
 
-> For an example of how to create custom shapes, see our [custom shapes example](https://github.com/tldraw/tldraw/tree/main/apps/examples/src/examples/CustomConfigExample).
+> For an example of how to create custom shapes, see our [custom shapes example](/examples/shapes/tools/custom-shape).
 
 ### Shape type