Update README with information about transports and platform availability

Author: mattt

README.md

@@ -6,28 +6,38 @@ Swift implementation of the [Model Context Protocol][mcp] (MCP).
 
 - Swift 6.0+ (Xcode 16+)
 
-## Platform Support
-
 | Platform | Minimum Version |
 |----------|----------------|
 | macOS | 13.0+ |
 | iOS / Mac Catalyst | 16.0+ |
 | watchOS | 9.0+ |
 | tvOS | 16.0+ |
 | visionOS | 1.0+ |
-| Linux | ✓ |
-| Windows | ✓ |
-
-> [!IMPORTANT]  
-> MCP's transport layer handles communication between clients and servers.
-> The Swift SDK supports multiple transport mechanisms,
-> with different platform availability:
->
-> * `StdioTransport` is available on Apple platforms 
->   and Linux distributions with glibc, such as
->   Ubuntu, Debian, Fedora, CentOS, or RHEL. 
->
-> * `NetworkTransport` is available only on Apple platforms.
+
+### Transports and Platform Availability
+
+MCP's transport layer handles communication between clients and servers. 
+The Swift SDK provides multiple built-in transports:
+
+- [`StdioTransport`](/Sources/MCP/Base/Transports/StdioTransport.swift):
+  Implements [stdio](https://modelcontextprotocol.io/specification/2025-03-26/basic/transports#stdio) transport.
+  Available on Apple platforms 
+  and Linux distributions with glibc (Ubuntu, Debian, Fedora, CentOS, RHEL).
+- [`HTTPClientTransport`](/Sources/MCP/Base/Transports/HTTPClientTransport.swift):
+  Implements [Streamable HTTP transport](https://modelcontextprotocol.io/specification/2025-03-26/basic/transports#streamable-http)
+  using Foundation [URL Loading System](https://developer.apple.com/documentation/foundation/url-loading-system) 
+- [`NetworkTransport`](/Sources/MCP/Base/Transports/NetworkTransport.swift):
+  Implements custom transport over TCP and UDP
+  using Apple's [Networking framework](https://developer.apple.com/documentation/network).
+  Available exclusively on Apple platforms.
+
+While the core library works on any platform supporting Swift 6 
+(including Linux and Windows), 
+running a client or server requires a compatible transport. 
+You can implement a custom transport for platforms without built-in support.
+
+For custom transport implementation details, 
+see the [`Transport` protocol](/Sources/MCP/Base/Transport.swift).
 
 ## Installation