docs: add DeepWiki badge to README

[cevheri]

Motivation & Benefits

• The DeepWiki badge gives a quick visual indicator of project health / status, improving the README’s usefulness and attractiveness.

DeepWiki Link: https://deepwiki.com/langchain-ai/new-langgraph-project

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This PR introduces two small but useful changes:

1. chore: Update .gitignore to include the .idea/ directory, so JetBrains IDE metadata is excluded from VCS.
2. docs: Add a DeepWiki badge to the README.md for automatic status display and better project visibility.

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Changes

• .gitignore
  • Added .idea/ to ignore list
• README.md
  • Inserted DeepWiki badge (auto-refresh badge)
  • Adjusted formatting to accommodate the badge

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Checklist

• .gitignore updated
• README badge added and visually aligned
• No breaking changes
• Documentation/guides updated (where relevant)

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If you like, I can also add badges for CI, coverage, or other useful project status indicators.

Let me know if you’d like adjustments!

[amirkiarafiei]

DeepWiki is useful and complementary to the existnig langgrpah docs for better understanding the project 👍