Help string for --pprof.

rtiow/src/renderer.rs

@@ -81,6 +81,7 @@ pub struct Opt {
     /// Select scene to render, one of: "bench", "book", "tutorial" "cube", "bvh", "test"
     #[structopt(long = "model", default_value = "test")]
     pub model: Model,
+    /// Path to store pprof profile data, i.e. /tmp/cpuprofile.pprof
     #[structopt(long = "pprof", parse(from_os_str))]
     pub pprof: Option<PathBuf>,
     /// Use acceleration data structure, may be BVH or kd-tree depending on scene.