No regular expression required in Notepad++. It has a function called "Column Editor". This allows you to insert characters and more importantly increasing numbers easily at the start of each line. I could try to explain it but the online manual does a far better job. You would do it in 2 steps, first add the number, then put the cursor back at the start of the line and add the text. The reference is at

https://npp-user-manual.org/docs/editing/#column-editor-dialog