Adds step-by-step instructions for installing from both brew and
the official tarball. Not sure if steps for installing from source
belong here, so left them out.
Fixes#1005
* Add meta author, description and generator tags
* Add Hugo version beside the logo and in the footer
* Suggest the user to run `go get -u -v` to update dependencies
* Requires Go 1.3+ rather than Go 1.1+
* Improve rendering/formatting in some places
* Add trailing slash to URLs where appropriate
* GitHub redirects all http requests to https, update accordingly