simple callsign sanity check

src/config.rs

@@ -35,7 +35,11 @@ pub struct Config {
 impl Config {
     pub fn load() -> anyhow::Result<Self> {
         let file_contents = read_conf_file()?;
-        let config = toml::from_str(&file_contents).context("parsing config file")?;
+        let config: Self = toml::from_str(&file_contents).context("parsing config file")?;
+
+        if config.callsign == "CHANGEME" {
+            bail!("Callsign is not configured in config file");
+        }
 
         Ok(config)
     }