These are the GOV.UK styleguides

So clarify that. Also, add a one-line description as per the README guidelines. Also, make markdown heading consistent.
Move the external links together

These are useful links to other styleguides. This is worth clarifying as it's not clear whether/how they are maintained. Could consider removing them from here.

I have not included the external link to the [wiki wiki](https://github.com/alphagov/wiki/wiki) for gem guidelines, as they should be here.
There are languages and tools

It's worthwhile separating the two as the contents of a style guide for how to use Git is very different to the type of content in a Ruby style guide.

Also, they are not headings, just links.
Move detail about origin of Ruby styleguide

It's more useful to keep that meta-information with the actual document.
Add missing links
Tidy and re-order
Replace unmaintained type and colour links

With govuk-elements, which is actively maintained and does a better job of explaining things.
Merge pull request #62 from alphagov/update-readme

Update README