Add descriptions for lexicon categories

[bellasalmonella]

This pull request the issue 'write descriptions for lexicon categories'.

Specifically, I have:

• Updated the 'description' property in the category JSON files for every chapter.
• Added corresponding English translation keys and their verbose descriptions to the en_us.json file.

If there are any specific requirements for writing style that I missed, please let me know and I can amend them.

[williewillus]

Nice writing! Did you check ingame how things look/if the text fits properly?

[TheRealWormbo]

Yup, very nice. The only thing that could probably be adjusted is the way the descriptions directly address the reader, as the rest of the lexicon text doesn't do that. (Except in the Alfheim intro, for lore reasons.)

[TheRealWormbo]

I had a look in-game now, and unfortunately many of the descriptions are a bit too long to fit into the reduced space of the category description page.

[TheRealWormbo]

I'm going to add simple, short descriptions for now. Feel free to reword yours to make them fit the page, so we can use those instead.