docs: add deepwiki badge to readme

[luyuzhe111]

Description

This PR adds the DeepWiki badge to README, so that the DeepWiki page for this repo can be automatically refreshed and Strands developers can always get up-to-date answers about this repo, which is growing very fast and gaining a lot of adoptions.

Related Issues

N/A

Documentation PR

N/A

Type of Change

Documentation update

Testing

How have you tested the change? Verify that the changes do not break functionality or introduce warnings in consuming repositories: agents-docs, agents-tools, agents-cli

• I ran hatch run prepare

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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