Add or update examples for some commands (#4521)

* chore: add or update examples for some commands

* chore: code formatting

crates/nu-command/src/date/now.rs

@@ -1,7 +1,7 @@
 use chrono::Local;
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
-use nu_protocol::{Category, IntoPipelineData, PipelineData, Signature, Value};
+use nu_protocol::{Category, Example, IntoPipelineData, PipelineData, Signature, Value};
 #[derive(Clone)]
 pub struct SubCommand;
 
@@ -33,4 +33,12 @@ impl Command for SubCommand {
         }
         .into_pipeline_data())
     }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            description: "Get the current date and display it in a given format string.",
+            example: r#"date now | date format "%Y-%m-%d %H:%M:%S""#,
+            result: None,
+        }]
+    }
 }