Since the game doesn't come with any support for achievements, you'll probably need a GUI for displaying them. I'd recommend checking out the other GUIs and basically just copy + replace stuff until it works.
You can use function clientCmdGameEnd (where the end game screen opens) to check for times for various levels. If you want anything more complicated than best time achievements then you're going to have to research how to detect when the player gets those achievements.
It's probably going to be quite a bit of work. You should strongly consider whether having achievements is necessary.
PQ in a nutshell
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