docs: add package list to main example

examples/main.rs

@@ -8,6 +8,12 @@ use tokio_gemini::certs::{
     verifier::{SelfsignedCert, SelfsignedCertVerifier},
 };
 
+//
+// cargo add tokio_gemini
+// cargo add tokio -F macros,rt-multi-thread,io-util,fs
+// cargo add dashmap
+//
+
 #[tokio::main]
 async fn main() -> Result<(), tokio_gemini::LibError> {
     let mut args = std::env::args();