[ko-KR] Preface translation

[EatChangmyeong]

I've translated the preface chapter into Korean (ko-KR); I'd also like to contribute to a few more chapters in the future.

A number of translation concerns:

• The term "Beziér curve" is typically translated into either "베지에 곡선" (~22,800 results in Google Search, with a "Did you mean 베지어 곡선?" suggestion) or "베지어 곡선" (~56,300 results); the former seems to be a more "correct" transliteration (Korean Wikipedia chose "베지에 곡선"), but the latter is more common. I decided to go with the former, but I can change this any time.
• The font I'm using here is Noto Sans Korean, more specifically a WOFF version in sangwoobae/noto-sans-korean-webfont. The font itself is licensed under OFL, and the repo is under Apache License 2.0.
• font-size is 17.2px for now but I'm not confident with this value.
• locale-strings.js is fully translated, with the exception of donationCTA, bitcoinHeading and bitcoinCTA.

PS: Thank you for the great work! I had to work with Beziér maths time to time and your primer always helped me a lot.

[Pomax]

Thank you so much for getting Korean translations started! If this is specifically the korean version of noto sans, let's make sure the filename indicates that too so it won't conflict with a future use of another language/locale-specific version of noto, though.

And of course: happy new year =)

[Pomax]

Hm, it looks like this might need a rebase, too, since the master branch got updated a few times. Would you be up for that?

[EatChangmyeong]

Actually I'm not used to how Git and GitHub works, but I'll try -- I'll let you know when I succeed.

[EatChangmyeong]

I just pulled your changes, do I need to run npm start again?

[Pomax]

generally yes, that'll generate updated .html files

[EatChangmyeong]

All done, is there something else I should do?

[Pomax]

Just one small thing and then this can be merged in.

[Pomax]

in it goes!