Migrate german styleguide from the docs.

[Ivorforce]

Add a new section for language-specific styleguides. We do have one already (german), which is currently hosted on the docs repository (https://github.com/godotengine/godot-docs/tree/master/_styleguides).

I propose 'officially' hosting them along the other style guides, such that they can be linked to. Previously, they existed only on the repo, but were not built into the website. We can also adapt the old style, if that's preferred.

[Mickeon]

This is fascinating. We have an Italian repository to serve a similar purpose, but having it directly tied to Godot's documentation would be a huge plus.

[Ivorforce]

This is fascinating. We have an Italian repository to serve a similar purpose, but having it directly tied to Godot's documentation would be a huge plus.

The main problem may be finding people who can review changes to these files, especially if we start accepting style guides for more languages.
I'm also a bit wary about having files in different languages, since it might be confusing for search results.

On the other hand, it makes translation style guides first class, making them findable for contributors. I'm not sure how easy the german style guide is to find in the folder it is current hidden in (on the docs repo).

[Mickeon]

Let it be known I'm not against it, personally, but it needs to be discussed way more thoroughly in chat. Ideally, but practically impossible, we would first need the German Godot community's opinion, then the consensus of most Godot communities in their specific languages, as well. And then some way to point to this styleguide, per-language.