replace absolute links with relative links for gatsbyjs.org docs (#2999)

* fix links for both gatsbyjs.org and github.com

These links have to function both within gatsbyjs.org and within github.com, so I think they should be written as inline HTML. The currently do not resolve correctly within gatsbyjs.org. #2998

* prefer relative links over absolute for docs

Author: Ben Forshey

docs/docs/gatsby-style-guide.md

@@ -15,7 +15,7 @@ We plan, write, and maintain these Guide articles on GitHub.
 
 # What are Guide articles?
 
-Guide articles can cover a broad range of topics. Please see the following examples: [tutorials](https://www.gatsbyjs.org/tutorial/part-one/), [code documentation](https://www.gatsbyjs.org/docs/browser-apis/), [explanatory articles](https://www.gatsbyjs.org/docs/prpl-pattern/), and [focused guides](https://www.gatsbyjs.org/docs/add-404-page/).
+Guide articles can cover a broad range of topics. Please see the following examples: [tutorials](/tutorial/part-one/), [code documentation](/docs/browser-apis/), [explanatory articles](/docs/prpl-pattern/), and [focused guides](/docs/add-404-page/).
 
 # What can I write an article about?