docs: add default log filename to documentation

- In addition, update docs for `ArcedNodeBuilder::set_log_file_path`

Author: enigbe

src/builder.rs

@@ -610,7 +610,7 @@ impl ArcedNodeBuilder {
 		self.inner.write().unwrap().set_storage_dir_path(storage_dir_path);
 	}
 
-	/// Sets the log dir path if logs need to live separate from the storage directory path.
+	/// Sets the log file path if logs need to live separate from the storage directory path.
 	pub fn set_log_file_path(&self, log_file_path: String) {
 		self.inner.write().unwrap().set_log_file_path(log_file_path);
 	}

src/config.rs

@@ -105,7 +105,8 @@ pub struct Config {
 	pub storage_dir_path: String,
 	/// The path where logs are stored.
 	///
-	/// If set to `None`, logs can be found in [`Config::storage_dir_path`] directory.
+	/// If set to `None`, logs can be found in `ldk_node.log` in the [`Config::storage_dir_path`]
+	/// directory.
 	pub log_file_path: Option<String>,
 	/// The used Bitcoin network.
 	pub network: Network,