Auto-Timestamp Google Sheet

I need a lightweight Google Apps Script added to my existing worksheet so that every time any of our 1-5 editors types a value into specified columns, a date-and-time stamp is written automatically. The stamp must appear in the format DD/MM/YYYY HH:MM and should never overwrite existing data in other columns.

Please deliver:
• A clean, well-commented script bound to the sheet
• Brief setup notes so I can choose which columns trigger the timestamp and adjust them later if needed

Once the script is live I’ll test by entering sample values; if the correct timestamp appears without lag or conflict, the job is done.