Add a description about NETWORK_ID

Author: majecty

server/README.md

@@ -35,6 +35,7 @@ Run
 
 Just run `codechain-agent-hub` in your shell. 
 To safely communicate with the Dashboard, please set the `PASSPHRASE` environment variable. The Dashboard program should use the same passphrase.
+Also, you should set `NETWORK_ID` environment variable to print the network id in log messages.
 
 When you are using the `PASSPHRASE` you should use SSL over the connection. If you don't use the SSL, the `PASSPHRASE` is open to the internet. 
 

server/src/daily_reporter.rs

@@ -13,7 +13,7 @@ pub fn start(
     db_service: DBServiceSender,
     agent_service: AgentServiceSender,
 ) -> thread::JoinHandle<()> {
-    let network_id = std::env::var("NETWORK_ID").unwrap();
+    let network_id = std::env::var("NETWORK_ID").expect("NETWORK_ID environment variable is needed");
 
     thread::Builder::new()
         .name("daily reporter".to_string())