Aside from putting that shebang line at the top of the file you want to run as a script, the file has to be saved as a NimScript file, namely use a .nims file ending.
someScript.nims
#!/usr/bin/env nim
echo "Hello from NimScript!"
echo defined(NimScript)
Run
and then in your terminal:
chmod +x someScript.nims
./someScript.nims
Run
and it should run just fine.
