expand on data in file spec

one_line_file_type_spec.md

@@ -22,6 +22,7 @@ The file should follow the following format:
 width (max 255)
 height (max 255)
 termination byte (255)
+data (x1 y1 x2 y2 ...)
 ```
 
 An example file converted from binary to text would looks something like this. Commas