Tempo marking

Best way is to simplywrite "Swing eighths" - that's how swing is normally notated anyhow. But if you do wish to use the triplet notation, see for example https://musescore.org/en/node/10570. If you do a search, you should find other threrads where people have posted their own graphics you can download and use.

I made the attached image, which IMHO is vastly superior to most of the options people have shared here. Add it to your score and scale to 25%. Here's what it looks like:

https://musescore.com/isaacweiss/la-vie-en-rose