Specify 'time' feature for Tokio crate addition (#3721)

Author: 4laoshiren

src/content/docs/learn/splashscreen.mdx

@@ -126,7 +126,7 @@ If you are not an advanced user it's **highly recommended** that you use the opt
     # Run this command where the `Cargo.toml` file is
     cd src-tauri
     # Add the Tokio crate
-    cargo add tokio
+    cargo add tokio -F time
     # Optionally go back to the top folder to keep developing
     # `tauri dev` can figure out where to run automatically
     cd ..