Re-add fixed-width size for image (#2485)

## Summary

@zanieb pointed out that the image is now comically large.

Author: charliermarsh

README.md

@@ -9,7 +9,7 @@ An extremely fast Python type checker and language server, written in Rust.
 <br />
 
 <p align="center">
-  <img alt="Shows a bar chart with benchmark results." src="https://raw.githubusercontent.com/astral-sh/ty/main/docs/assets/ty-benchmark-cli.svg">
+  <img alt="Shows a bar chart with benchmark results." width="500px" src="https://raw.githubusercontent.com/astral-sh/ty/main/docs/assets/ty-benchmark-cli.svg">
 </p>
 
 <p align="center">