Improve error messages in configuration and initialization

Clarify the error message when no configuration file is found by suggesting using the `--help` option or trying `rusty-buddy init`. This improves user guidance when encountering an error.

src/main.rs

@@ -60,7 +60,9 @@ async fn main() {
         run_init_command().await.unwrap();
     }
     if !check_environment() {
-        error!("No configuration file found.");
+        eprintln!(
+            "No configuration file found. Use --help for more information or try rusty-buddy init."
+        );
         std::process::exit(1);
     }
     if let Err(e) = setup_logging() {

src/provider/openai/openai_interface.rs

@@ -225,6 +225,11 @@ fn truncate_to_max_bytes(s: &str, max_bytes: usize) -> &str {
 impl OpenAIInterface {
     pub fn new(model: String, timeout_secs: u64) -> Self {
         dotenv().ok();
+        // Check if the OPENAI_KEY is set in the environment
+        if env::var("OPENAI_KEY").is_err() {
+            eprintln!("Error: The environment variable 'OPENAI_KEY' must be set.");
+            std::process::exit(1);
+        }
 
         OpenAIInterface {
             model,