add palette name and colour count for GIMP palette

src/palette.rs

@@ -101,8 +101,11 @@ impl Palette {
             )
         }).collect();
 
-        // todo re-insert original comments
-        format!("GIMP Palette\r\n{}\r\n", colours.join("\r\n"))
+        // todo fix palette description? does it matter?
+        format!(
+            "GIMP Palette\r\n#Palette Name: {}\r\n#Colors: {}\r\n{}\r\n",
+            self.name, colours.len(), colours.join("\r\n")
+        )
     }
 
     /// Paint.net .txt format