docs: add iOS SDK build and integration instructions (fixes #769)

[samerzumot]

Description

Fixes #769.

This PR adds comprehensive iOS SDK build, installation, and app integration instructions to the BrainFlow documentation, modeled after the existing Android guide.

Context & Evaluation

• Issue iOS SDK and instructions #769 ("iOS SDK and instructions"): While the Apple XCFramework build infrastructure (tools/apple/build_xcframeworks.sh, tools/apple/regenerate_artifacts.sh) and demo app (swift_package/examples/apps/ios/BrainFlowiOSDemo) were already present in the codebase, docs/BuildBrainFlow.rst previously lacked a dedicated iOS section parallel to the Android documentation.
• Issue Add swift binding #327 ("Add swift binding"): Swift language bindings (swift_package/) are already complete with full API parity (BoardShim, DataFilter, MLModel) and CI tests, so Add swift binding #327 can be closed as completed.

Changes Made

1. docs/BuildBrainFlow.rst:

   • Added a dedicated, top-level iOS section (:ref:ios-label``) covering:
     • Swift Package Manager (Recommended): Precompiled remote Swift package (BrainFlowSwiftPackageRemote with checksums) and local binary package (BrainFlowSwiftBinaryPackage).
     • Direct XCFramework Integration: Embedding and code-signing BoardController.xcframework, DataHandler.xcframework, and MLModule.xcframework in Xcode.
     • Permissions and Privacy Configuration: CoreBluetooth keys (NSBluetoothAlwaysUsageDescription, NSBluetoothPeripheralUsageDescription), network access, and PrivacyInfo.xcprivacy manifest requirements.
     • Quick Start Example: Minimal, working Swift code showing session initialization, streaming, and signal processing (DataFilter.perform_lowpass).
     • Compilation from Source: Step-by-step instructions for tools/apple/build_xcframeworks.sh and tools/apple/regenerate_artifacts.sh, artifact layout (XCFrameworks/, BrainFlowSwiftBinaryPackage, SwiftPMArtifacts/), and feature flags (BRAINFLOW_APPLE_BUILD_BLE=ON).
     • iOS Demo Application: Guide to running swift_package/examples/apps/ios/BrainFlowiOSDemo in Xcode and simulator (including --autorun smoke testing).
     • References: Links to AppleBinaryDistribution.rst, AppStoreReadiness.rst, and SwiftAPIParity.rst.
   • Added a cross-reference link to :ref:ios-label`` in the Swift precompiled libraries section.

2. docs/SupportedBoards.rst:

   • Added - iOS to the supported platforms list for Streaming Board, Synthetic Board, and Playback Board.

Verification

• Validated swift_package/Package.swift with swift package dump-package.
• Verified scheme resolution and package graph for the iOS demo project with xcodebuild -list -project swift_package/examples/apps/ios/BrainFlowiOSDemo/BrainFlowiOSDemo.xcodeproj.
• Verified CLI options and environment variables in tools/apple/build_xcframeworks.sh -h.