feat: add --help and --version flags

fixes: https://github.com/scsibug/nostr-rs-relay/issues/42

src/main.rs

@@ -18,6 +18,18 @@ fn db_from_args(args: &[String]) -> Option<String> {
     None
 }
 
+fn print_version() {
+    println!("{} v{}", env!("CARGO_PKG_NAME"), env!("CARGO_PKG_VERSION"));
+}
+
+fn print_help() {
+    println!("Usage: nostr-rs-relay [OPTION]...\n");
+    println!("Options:");
+    println!("  --help              Show this help message and exit");
+    println!("  --version           Show version information and exit");
+    println!("  --db <directory>    Use the <directory> as the location of the database");
+}
+
 /// Start running a Nostr relay server.
 fn main() {
     // setup tracing
@@ -25,6 +37,21 @@ fn main() {
     info!("Starting up from main");
     // get database directory from args
     let args: Vec<String> = env::args().collect();
+
+    let help_flag: bool = args.contains(&"--help".to_owned());
+    // if --help flag was passed, display help and exit
+    if help_flag {
+        print_help();
+        return;
+    }
+
+    let version_flag: bool = args.contains(&"--version".to_owned());
+    // if --version flag was passed, display version and exit
+    if version_flag {
+        print_version();
+        return;
+    }
+
     let db_dir: Option<String> = db_from_args(&args);
     // configure settings from config.toml
     // replace default settings with those read from config.toml