docs: update architecture diagram (#1888)

## Description

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> impact, along with a summary of the solution

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- [ ] Make sure you reviewed

[CONTRIBUTING.md](https://github.com/googleapis/genai-toolbox/blob/main/CONTRIBUTING.md)
- [ ] Make sure to open an issue as a

[bug/issue](https://github.com/googleapis/genai-toolbox/issues/new/choose)
  before writing your code! That way we can discuss the change, evaluate
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🛠️ Fixes #<issue_number_goes_here>

README.md

@@ -98,7 +98,9 @@ centralized location to store and update tools, allowing you to share tools
 between agents and applications and update those tools without necessarily
 redeploying your application.
 
-![architecture](./docs/en/getting-started/introduction/architecture.png)
+<p align="center">
+<img src="./docs/en/getting-started/introduction/architecture.png" alt="architecture" width="50%"/>
+</p>
 
 ## Getting Started