eprintln init_logger failure (may need redir if it's flushed away)

and add a description on logging

docs/config_file.md

@@ -29,3 +29,9 @@ Run the following command to generate a config file with the default parameters:
 ```sh
 navi info config-example > "$(navi info config-path)"
 ```
+
+### Logging
+
+The log file will be created under the same directory where the config locates.
+
+And you can use the `RUST_LOG` env to set the log level, e.g. `RUST_LOG=debug navi`.

src/bin/main.rs

@@ -24,8 +24,11 @@ impl FileAnIssue {
     }
 }
 
-fn main() -> Result<(), anyhow::Error> {
+fn main() -> anyhow::Result<()> {
-    init_logger()?;
+    if let Err(err) = init_logger() {
+        // may need redir stderr to a file to show this log initialization error
+        eprintln!("failed to initialize logging: {err:?}");
+    }
     navi::handle().map_err(|e| {
         error!("{e:?}");
         FileAnIssue::new(e).into()