Update cursor.mdx (#1331)

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> [!IMPORTANT]
> Adds documentation in `cursor.mdx` for Cursor rules to write BAML with
a link to a `.cursorrules` file.
> 
>   - **Documentation**:
> - Adds a section in `cursor.mdx` about Cursor rules for writing BAML.
> - Provides a link to a `.cursorrules` file to aid in writing BAML
prompts.
> 
> <sup>This description was created by </sup>[<img alt="Ellipsis"
src="https://img.shields.io/badge/Ellipsis-blue?color=175173">](https://www.ellipsis.dev?ref=BoundaryML%2Fbaml&utm_source=github&utm_medium=referral)<sup>
for c1f43e9. It will automatically
update as commits are pushed.</sup>

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fern/01-guide/01-editors/cursor.mdx

@@ -5,4 +5,7 @@ Refer to the [Cursor Extension Installation Guide](https://www.cursor.com/how-to
 
 <Warning>
 You may need to update BAML extension manually using the process above. Auto-update does not seem to be working well for many extensions in Cursor.
-</Warning>
+</Warning>
+
+### Cursor Rules to write BAML
+We created a [.cursorrules file for BAML](https://gist.github.com/aaronvg/b4f590f59b13dcfd79721239128ec208), to aid Cursor in writing BAML prompts. Feel free to edit this however you like!