Heya

I'm still somewhat new to Nix and NixOS and I'd like to suggest a version bump for an existing package. (And create the PR for that myself, not just file an issue.)

I've made the change in my local clone of https://github.com/NixOS/nixpkgs and successfully built it with
```
nix-shell -p nox --run "nox-review wip"
```

(End of output was
```
[...]

checking for references to /tmp/nix-build-qgis-2.18.14.drv-0 in /nix/store/c4g94hvhix61gq1dblcpvnh929l7v1jl-qgis-2.18.14...
/nix/store/c4g94hvhix61gq1dblcpvnh929l7v1jl-qgis-2.18.14
Result in /run/user/1000/nox-review-6a6gyon0
insgesamt 0
lrwxrwxrwx 1 das-g users 56 22. Nov 17:29 result -> /nix/store/c4g94hvhix61gq1dblcpvnh929l7v1jl-qgis-2.18.14

```
)

Now what?

I'd like to test the resulting application before creating the PR. How do I switch into an environment that has it?