Update TODO.md

TODO.md

@@ -99,3 +99,4 @@ Ideas and wishlist
 8. Add `--image` flag that would allow to build only one image, by it's name, which would support debugging of issues, without the need to rebuild all the images again and again
 9. Add `--workdir` flag, to allow defining where temporary templates or tar packages should be placed as current dir or Dockerfiles dir might not be preffered in some situations
 10. Add `--progress` flag, that would enable progressbar, maybe: https://github.com/schollz/progressbar
+11. Templating on Dockerfiles should happen only if they have `.tpl` extension