I'll admit I was one of the people saying that it should be attack instead of capture. But after the RC (many months ago) I hated attack instead of capture.
They were moved to gui/reference/tips/texts/ a while ago: https://gitea.wildfiregames.com/0ad/0ad/src/branch/main/binaries/data/mods/public/gui/reference/tips/texts
No, I don't think so. I guess I could add one, but I'm not sure if it's the right place teach it. I mean, capturing is not really a 'trick', is it? It's a core game mechanic. Maybe it should be included in the tutorial instead.