Add description for `@inngest/middleware-encryption` package

[jpwilliams]

Summary

Adds a description to the @inngest/middleware-encryption package.

Checklist

• [ ] Added a docs PR that references this PR N/A
• [ ] Added unit/integration tests N/A
• [x] Added changesets if applicable

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: e4e202abde3489071646cbf5382899462fa3c62f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

| Name | Type | | ------------------------------ | ----- | | @inngest/middleware-encryption | Patch |

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