Check if downloads badge points to something useful

We have 

```
[![Downloads - total](https://cranlogs.r-pkg.org/badges/grand-total/RcppTskit)](https://cranlogs.r-pkg.org/badges/grand-total/RcppTskit)
```

which links to https://cranlogs.r-pkg.org/badges/grand-total/RcppTskit, but I only see a badge there at the time of writing this issue (maybe counting has not yet started on CRAN?).