document and improve Quick numbers metrics

### Describe the issue

In this page https://translate.fedoraproject.org/stats/
I see these results, including 1200 contributors for the fedora translation platform:

When I extract the "Contributor stats" metrics for the current year from https://translate.fedoraproject.org/#reports I get 306 users.

I am fine with this metric to be different with the report, but I would like to have a description of the metrics at least in the Weblate documentation, and if possible as a tooltip.

Also, having also the raw number and the percentage variation in parenthesis would make the measure more explicit to me.

### I already tried

- [x] I've read and searched [the documentation](https://docs.weblate.org/).
- [x] I've searched for similar filed issues in this repository.

### Steps to reproduce the behavior

go to https://translate.fedoraproject.org/stats/ and see the values
access https://translate.fedoraproject.org/#reports and export metrics for current year

### Expected behavior

_No response_

### Screenshots

_No response_

### Exception traceback

```pytb

```

### How do you run Weblate?

_No response_

### Weblate versions

_No response_

### Weblate deploy checks

```shell

```

### Additional context

_No response_