docs(readme): update desktop screenshot and align its caption

Author: waleedlatif1

README.md

@@ -72,7 +72,7 @@ macOS 12+, Apple Silicon and Intel. See the [desktop docs](https://docs.sim.ai/d
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       <img src="apps/sim/public/static/readme-desktop.png" alt="Sim Desktop — Chat on the left, the built-in browser on the right" width="100%"/>
-      <p align="center"><b>Desktop</b> — a built-in browser and terminal your agents can drive</p>
+      <p align="center"><b>Desktop</b> — Sim on your Mac, browser and terminal included</p>
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