Note about feature flags for uefi book

Author: stillinbeta

book/src/tutorial/app.md

@@ -19,6 +19,16 @@ Add a few dependencies:
 cargo add log uefi
 ```
 
+You'll need to add some feature flags and configuration to Cargo.toml as well:
+```toml
+[dependencies]
+log = "0.4.21"
+uefi = { version = "0.28.0", features = [ "panic_handler", "logger" ] }
+
+[profile.dev]
+panic="abort"
+```
+
 Replace the contents of `src/main.rs` with this:
 
 ```rust