chore(docs): refine part 1, 2

Signed-off-by: Alex Chi <iskyzh@gmail.com>

xtask/src/main.rs

@@ -8,6 +8,7 @@ use duct::cmd;
 #[derive(clap::Subcommand, Debug)]
 enum CopyTestAction {
     Day1,
+    Day2,
 }
 
 #[derive(clap::Subcommand, Debug)]
@@ -132,6 +133,14 @@ fn copy_test_case(test: CopyTestAction) -> Result<()> {
             )
             .run()?;
         }
+        CopyTestAction::Day2 => {
+            cmd!(
+                "cp",
+                "mini-lsm/src/table/tests.rs",
+                "mini-lsm-starter/src/table/tests.rs"
+            )
+            .run()?;
+        }
     }
     Ok(())
 }