chore: add TierRegistry address

[horsefacts]

Change Summary

Add deployed TierRegistry address

Merge Checklist

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• The PR title adheres to the conventional commits standard
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PR-Codex overview

This PR updates the README.md file to correct the capitalization of "Farcaster" in several instances, adds a new section for the Tier Registry, and includes information about the v3.2 contracts audit.

Detailed summary

• Capitalized "Farcaster" in descriptions of Id Registry, Id Gateway, and Fname Resolver.
• Added Tier Registry contract description and address under "Base Mainnet".
• Included audit information for v3.2 contracts reviewed by 0xMacro.

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[github-actions]

Coverage after merging horsefacts/add-tier-registry-address into main will be

100.00%

Coverage Report

File	Stmts	Branches	Funcs	Lines	Uncovered Lines
src
Bundler.sol	100%	100%	100%	100%
BundlerV1.sol	100%	100%	100%	100%
FnameResolver.sol	100%	100%	100%	100%
IdGateway.sol	100%	100%	100%	100%
IdRegistry.sol	100%	100%	100%	100%
KeyGateway.sol	100%	100%	100%	100%
KeyRegistry.sol	100%	100%	100%	100%
RecoveryProxy.sol	100%	100%	100%	100%
StorageRegistry.sol	100%	100%	100%	100%
TierRegistry.sol	100%	100%	100%	100%
src/abstract
EIP712.sol	100%	100%	100%	100%
Guardians.sol	100%	100%	100%	100%
Migration.sol	100%	100%	100%	100%
Nonces.sol	100%	100%	100%	100%
Signatures.sol	100%	100%	100%	100%
src/validators
SignedKeyRequestValidator.sol	100%	100%	100%	100%