How about appending the file contents instead of replacing them？

[chouchouji]

Reason

I set some commands in commit-msg hook by myself. When I use this package, it will rewrite commit-msg file if I set that hook.

Suggestion

How about replacing writeFileSync with appendFileSync?

Code

The source code position is https://github.com/toplenboren/simple-git-hooks/blob/master/simple-git-hooks.js#L204