[ko] update chapter 1

This commit improves the Korean translation of the first two paragraphs
in Chapter 1. It makes the sentences sound more natural and removes the
wrong clause in the first paragragh which says there will be an
explanation in this chapter for how to set up a Git server, which is not
true.
Merge pull request #849 from clee704/ko-contents

[ko] update chapter 1
[ko] add a translation guide
[ko] update chapter 1

Improve the overall translation quality by conveying the meaning of the
original text more accurately, avoiding colloquial expressions, using
a more consistent writing style, etc.