Add comments from the C tutorial to basic-tutorial-1

tutorials/src/bin/basic-tutorial-1.rs

@@ -4,16 +4,19 @@ use gst::prelude::*;
 use std::u64;
 
 fn main() {
+    // Initialize GStreamer
     gst::init().unwrap();
 
+    // Build the pipeline
     let uri = "https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.webm";
     let pipeline = gst::parse_launch(&format!("playbin uri={}", uri)).unwrap();
 
+    // Start playing
     let ret = pipeline.set_state(gst::State::Playing);
     assert_ne!(ret, gst::StateChangeReturn::Failure);
 
+    // Wait until error or EOS
     let bus = pipeline.get_bus().unwrap();
-
     loop {
         use gst::MessageView;
 
@@ -37,6 +40,7 @@ fn main() {
         }
     }
 
+    // Shutdown pipeline
     let ret = pipeline.set_state(gst::State::Null);
     assert_ne!(ret, gst::StateChangeReturn::Failure);
 }