Simply do the usual command:
cargo run --example <example_name>
This will use the default asynchronous runtime (currently tokio). If you want to run them using async-std instead of tokio, do the following:
cargo run --example <example_name> --no-default-features --features async-std-runtime
zeromq works on both tokio and async-std, so we have added some helper code to get things working with either async runtime. In your code you often won't need to care about this, in which case just use tokio::main or async_std::main as normal instead of async_helpers::main.