Add --features flag to README examples

When running locally, the `cargo run`/`cargo playdate run` examples in
the README failed to compile due to missing required features. Hence,
add the relevant flag to all examples to ensure that they build and run
correctly, assuming the rest of the pre-requisites have been met.

README.md

@@ -41,14 +41,14 @@ Follow the instructions for:
 
 Run example:
 ```bash
-cargo run -p=cargo-playdate -- run -p=playdate-controls --example=buttons
+cargo run -p=cargo-playdate -- run -p=playdate-controls --example=buttons --features="sys/lang-items sys/entry-point"
 ```
 
 Install `cargo-playdate` and build & run another example:
 ```bash
 cargo install cargo-playdate
-cargo playdate run -p=playdate-sound --example=sp
-cargo playdate run -p=playdate-sound --example=sp --device
+cargo playdate run -p=playdate-sound --example=sp --features="sys/lang-items sys/entry-point"
+cargo playdate run -p=playdate-sound --example=sp --features="sys/lang-items sys/entry-point" --device
 ```
 
 ### Demo