add guides page

[maelle]

Fix #1161

New guides page, very easy layout: same as resources page.

Regarding the resources page's ordering, the resources appear in the same order as in the JSON file. Any suggestion on how to change the ordering? Or should the layout be changed (more involved)?

@yabellini The blog guide is missing from the Spanish JSON, but it hasn't been translated. Should we add it anyway? In that case could you please add the JSON entry to this PR? The contribution guide is there but is only in English too.

What other guides are missing? The new one for first time contributors?

[noamross]

I think the resources page could use a little hierarchical layout into sections.

The stats development guide could be added, too.

[yabellini]

It is a good idea to add all our guidelines even if they are not translated to the Spanish list. We can keep the title in English to signal that we haven't translated that content yet (perhaps even spark someone to start the translation).

[yabellini]

The one for first-time contributors needs to be reviewed by someone else before we make it public. Right @steffilazerte ?

[maelle]

Something like that? But what categories? The one I called "content" is a bit of a catch-all.

This is only a preview, if we go for this design I'd add translation to the Spanish page.