docs: add CNAME initialization examples for iOS and Android

[rmi22186]

Background

mParticle Flutter PR #73 added README examples for configuring a custom CNAME endpoint without any new Dart API — Flutter consumers initialise the mParticle SDK natively from their AppDelegate / Application class and wire MPNetworkOptions.customBaseURL / NetworkOptions.withNetworkOptions directly. React Native takes the same approach (no runtime JS bridge; only an Expo config plugin for build-time codegen). Cordova consumers initialise the same way, so a docs-only change matches.

What's changed

• README iOS section: MPNetworkOptions.customBaseURL snippet (Swift + Objective-C) inserted after the standard init example.
• README Android section: NetworkOptions.withNetworkOptions snippet (Java + Kotlin) inserted after the standard init example.
• CHANGELOG.md [Unreleased] entry under Added.

No JS API, no native bridge changes, no dependency bumps.

🤖 Generated with Claude Code

[cursor]

PR Summary

Low Risk
Documentation-only changes with no runtime, bridge, or dependency updates in this diff.

Overview
Documents how Cordova apps can point the native mParticle SDK at a custom CNAME during startup (still done in AppDelegate / Application.onCreate, not via JavaScript).

The README gains optional snippets after the existing iOS and Android init examples: Swift and Objective-C set MPNetworkOptions.customBaseURL on mParticleOptions, and Java/Kotlin use NetworkOptions.withNetworkOptions(...). CHANGELOG.md records the new README examples under [Unreleased].

^{Reviewed by Cursor Bugbot for commit 50e1573. Bugbot is set up for automated code reviews on this repo. Configure here.}

[rmi22186]

Docs only change, so build/test failure is not an issue - this should be fixed in shoppable-ads branch.