Add example that exercises decoding (no output)

examples/decode.rs

@@ -0,0 +1,19 @@
+use tiff::decoder::Decoder;
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let Some(image) = std::env::args_os().nth(1) else {
+        eprintln!("Usage: decode FILE");
+        return Ok(());
+    };
+
+    let file = std::fs::File::open(image)?;
+    let io = std::io::BufReader::new(file);
+    let mut reader = Decoder::new(io)?;
+
+    while {
+        reader.read_image()?;
+        reader.more_images()
+    } {}
+
+    Ok(())
+}