DESCRIPTION: Please add URL and BugReports

Please consider adding:

```
URL: https://github.com/ddalthorp/GenEst
BugReports: https://github.com/ddalthorp/GenEst/issues
```

to your DESCRIPTION file, so it's easy to find this repo from <https://cran.r-project.org/package=GenEst> and `bug.report(package = "GenEst")`.