`a.out` linux kernel support removed on linux 5.19

document uses `a.out`

https://springql.github.io/get-started/write-basic-apps/
```
LD_LIBRARY_PATH=. ./a.out
```

Linux kernel 5.19 not supports `a.out` executable.
see: https://www.phoronix.com/scan.php?page=news_item&px=Linux-5.19-Drops-x86-a.out
