Counter example in crates/rmcp/README.md does not compile

[RobJellinghaus]

Describe the bug
The example in crates/rmcp/README.md does not build with rmcp 0.6.0.

To Reproduce
Steps to reproduce the behavior:

1. Copy the code into src/main.rs in a new counter project
2. cargo build

Expected behavior
It builds successfully.

Logs
The errors actually observed (edited for brevity):

error: cannot find attribute `tool_handler` in this scope
 --> src/main.rs:39:3
39 | #[tool_handler]
 | ^^^^^^^^^^^^
help: consider importing one of these attribute macros
1 + use rmcp::tool_handler;
1 + use rmcp_macros::tool_handler;

error[E0405]: cannot find trait `Future` in this scope
 --> src/main.rs:20:5
20 | #[tool(description = "Increment the counter by 1")]
 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not found in this scope
 = note: this error originates in the attribute macro `tool` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider importing this trait
1 + use std::future::Future;

warning: unused import: `handler::server::tool::ToolCallContext`
 --> src/main.rs:1:94
1 | ...:*, tool, tool_router, transport::stdio, handler::server::tool::ToolCallContext, handler::server::router::tool::ToolRout...
 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 = note: `#[warn(unused_imports)]` on by default

Additional context
I will make a PR to fix this once I verify the counter server works locally under Claude Code.