Update the Identity-Crisis readme file.

[kbrown9]

Changes proposed in this Pull Request:

• Update the Identity Crisis package's readme file to include instructions on using the Config package to initialize the package.

Jetpack product discussion

• n/a

Does this pull request change what data or activity we track or use?

• no

Testing instructions:

• n/a - just a doc change.

[github-actions]

Thank you for your PR!

When contributing to Jetpack, we have a few suggestions that can help us test and review your patch:

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• ✅ Add changelog entries to affected projects
  

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