Documentation change for article tab title in the Admin

[thenetexperts]

Not a big deal, but I stumbled ;)

On the documentation page regarding article type translation the filename (admin.en.json) should be admin.en.yml.

EDIT: Nevermind, I just checked and sulu seems to use the .json format for translation files. So it's fine.

I would also put the reference to the translation file before the code snippet.