Add dictionary download links

[austinbutler]

The guide mentions StarDict and dictd, but there's no mention of places to get these. I avoided StarDict since it's not natively supported, so went looking for DICT/dictd format dictionaries. It's somewhat difficult to search for since "dict" is very generic and a lot of the results for "dictd" end up being Debian packages and such. I eventually ended up at the Arch wiki for dictd, which lead me to all the AUR dictd packages, which finally lead me to two sources that seem pretty good.

All that is to say, it's a bit of a hassle to figure this all out from scratch. So this PR tries to fill that gap a little more to make it less confusing. Personally I ended up going with the English-only Wikitionary dict from dictinfo.com and it seems to be working well. If there are better sources, though, I'd love to hear.

[foldfree]

I've found this repository that convert wiktionary dictionaries to stardict format, and then in Plato, there is a script that automatically convert it to dictd when the reader is launched.
The quality is better than the Oxford dictionary in my opinion. There is a guide to add your own language for those that wish to do so and the CC license makes it safe to share and distribute. I think it's a must personally.
Could there even be an option to download it within the app like the kobo reader does?

There was a tiny issue about the conversion script with it but baskerville just fixed it. So check if your conversion script is updated before testing it.