update generate_readme.py

* Add shebang to explicitly state which Python version the script
  needs.

scripts/generate_readme.py

@@ -1,3 +1,5 @@
+#!/usr/bin/python3
+
 from pathlib import Path
 
 def generate_img_tag(file):
@@ -11,4 +13,4 @@ if __name__ == "__main__":
         f.write("# Homer Icons\n\n")
         f.write("[Homer Dashboard](https://github.com/bastienwirtz/homer)\n\n")
         f.write(" ".join(img_tags))
-        f.write("\n")
+        f.write("\n")