Add a missing category feature to the sine example

plugins/examples/sine/src/lib.rs

@@ -202,6 +202,7 @@ impl ClapPlugin for Sine {
     const CLAP_MANUAL_URL: Option<&'static str> = Some(Self::URL);
     const CLAP_SUPPORT_URL: Option<&'static str> = None;
     const CLAP_FEATURES: &'static [ClapFeature] = &[
+        ClapFeature::Instrument,
         ClapFeature::Synthesizer,
         ClapFeature::Stereo,
         ClapFeature::Mono,