The options basically boil down to either:
- Having them work on static files which then get integrated by a backend developer (only really a reasonable option if you are farming out frontend work to a design agency without having them perform ongoing maintenance).
- Someone else setting up a development environment for them
- Having them setting up the dev environment while making it as easy as possible for them
The latter approach would typically involve clear, step-by-step instructions and a virtual machine image that comes largely preconfigured, possibly combined with a tool like vagrant or salt stack.