content: add info about the ripple effect duration

_Original issue by @distante on [2020-08-16T08:46:00Z](https://github.com/ionic-team/ionic-framework/issues/21922)_

# Documentation

The ripple effect duration used in components like `ion-button` is not documented. It would be useful for some developers that want to trigger some animation orchestration starting with a button click.

---

I can do a PR for this but I am not sure which duration this effect has. From the [source code I would say something like `325ms`](https://github.com/ionic-team/ionic-framework/blob/master/core/src/components/ripple-effect/ripple-effect.tsx#L66) but I am not really sure.
```
setTimeout(() => {
resolve(() => {
removeRipple(div);
});
}, 225 + 100);
```

Extra: what does that 225 and 100 mean?