chore: fix email address in readme (#2397)

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> [!IMPORTANT]
> Fix email link in `README.md` by adding `mailto:` protocol for proper
functionality.
> 
>   - **README.md**:
> - Fix email link by adding `mailto:` protocol to
`[email protected]` for proper email functionality.
> 
> <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 cf6e20f. You can
[customize](https://app.ellipsis.dev/BoundaryML/settings/summaries) this
summary. It will automatically update as commits are pushed.</sup>

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Author: sxlijin

README.md

@@ -236,7 +236,7 @@ Made with ❤️ by Boundary
 
 HQ in Seattle, WA
 
-P.S. We're hiring for software engineers that love rust. [Email us]([email protected]) or reach out on [discord](https://discord.gg/ENtBB6kkXH)!
+P.S. We're hiring for software engineers that love rust. [Email us](mailto:[email protected]) or reach out on [discord](https://discord.gg/ENtBB6kkXH)!
 
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