adding rustdoc

substrate/client/cli/src/commands/export_chain_spec_cmd.rs

@@ -56,6 +56,8 @@ pub struct ExportChainSpecCmd {
 }
 
 impl ExportChainSpecCmd {
+	/// Run the export-chain-spec command
+
 	pub fn run(&self, spec: &Box<dyn ChainSpec>) -> Result<()> {
 		let json = chain_ops::build_spec(spec.as_ref(), self.raw)?;
 		if let Some(ref path) = self.output {