Add comprehensive README.mbt.md documentation for HTTP and Process packages

[bobzhang]

This PR adds comprehensive, executable documentation for the HTTP and Process packages in the form of README.mbt.md files.

Changes

• Added HTTP package README.mbt.md with 19 executable test examples
• Added Process package README.mbt.md with 24 executable test examples
• Created README.md symlinks for both packages
• All tests passing (43/43 README tests, 49/49 total http+process tests)

HTTP Package Coverage

The HTTP documentation includes comprehensive examples for:

HTTP Client Usage

• Quick Start: Simple GET requests with and without custom headers
• One-Shot Requests: GET, POST, and PUT operations for single-use connections
• Persistent Connections: Connection reuse, HTTPS support, custom ports
• Request Methods: Detailed examples for GET, POST, PUT operations
• Custom Headers: Persistent headers on client and per-request headers
• Request/Response Bodies: Manual body sending, reading headers, skipping bodies

Reference Documentation

• Types Reference: Protocol enum and Response structure
• Error Handling: Examples for invalid URLs and connection errors
• Best Practices: Guidelines for proper connection management and error handling

Process Package Coverage

The Process documentation includes comprehensive examples for:

Process Management

• Quick Start: Simple command execution and exit code handling
• Output Collection: Collect stdout, stderr, both streams, or merged output
• I/O with Pipes: Reading from and writing to processes
• File Redirection: Input from files, output to files, file-to-file operations
• Environment Variables: Setting custom env vars, isolated environments
• Working Directory: Changing process working directory
• Async Management: Spawn and wait, orphan processes with delayed waiting
• Advanced Usage: Merge output streams, multiple processes sharing pipes

Reference Documentation

• Types Reference: ProcessInput and ProcessOutput traits
• Best Practices: Guidelines for pipe management and error handling
• Error Handling: Examples for command failures and exit codes

Testing

All code examples are executable and verified with:

• moon check for type checking
• moon test for runtime verification
• Black-box testing approach using @http and @process notation

This follows the same documentation approach as the fs package README.

[Guest0x0]

Is the process part the same as #125?