docs: add Apple Pay entitlement and Google Pay merchant ID prerequisites to README

[arstiefel]

Description

Adds prerequisite documentation for Apple Pay and Google Pay integration to the README. The Apple Pay section explains that developers must configure the Apple Pay entitlement with their Apple-registered merchant identifier (distinct from the Bolt publishable key), with setup instructions for both Xcode and Expo. The Google Pay section documents the requirement for a Google Pay merchant ID from the Business Console and notes that testing does not require a valid ID.

Testing

Documentation-only change — no code modified. Verify that the new "Prerequisites" and "Usage" subsections render correctly in GitHub Markdown and that the linked URLs (Apple Developer portal, Google Pay Business Console) are valid.

Security Review

Important

A security review is required for every PR in this repository to comply with PCI requirements.

• I have considered and reviewed security implications of this PR and included the summary below.

Security Impact Summary

No security-sensitive changes. This PR only adds documentation to the README. It does not touch authentication, authorization, payment flows, user data handling, or external integrations.

[snyk-io]

✅ Snyk checks have passed. No issues have been found so far.

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✅	Code Security	0	0	0	0	0 issues

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