Improve documentation about storage.

Also add related FAQs (including the ZFS bug).

Add roadmap documentation.

Update 'random-example' section.

1) Use https to clone 'client_golang' repository, like the 'prometheus'
   repository.
2) Update build instructions to specify 'example_random' target instead
   of 'random_example'. I updated the sample configs, too.

Use a protocol-relative URL to load Google Fonts

Add Docker install instructions

promdash is more useful for most users

Use new makefile to build target, doesn't depend on go being setup.

Don't expect users to know what screen is.

Make it clear what the full config is.

Expand faq.