docs(readme): add -p mcp-server-examples to build command

[tanish111]

Updated the build command to specify the package for the MCP server examples.

Motivation and Context

The cargo build --release --example servers_counter_stdio command in the README failed when run from either the workspace root or the examples/ directory. This is because the workspace's default-members only includes crates/rmcp and crates/rmcp-macros, so Cargo cannot resolve the example without an explicit package target. The fix adds -p mcp-server-examples to correctly scope the build command.

How Has This Been Tested?

Ran the original command (cargo build --release --example servers_counter_stdio) from both the workspace root and examples/ — confirmed it fails with error: no example target named.
Ran the updated command (cargo build --release -p mcp-server-examples --example servers_counter_stdio) from the workspace root — confirmed it builds successfully and produces the binary at target/release/examples/servers_counter_stdio.

Breaking Changes

NA

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

NA

[tanish111]

@alexhancock docs change.

[alexhancock]

you'll need to adjust the commit message to adhere to conventional commit format

i've also added a linter in main for this