[ja] Rename README to README.md
[ja] Update README.md
[ja] Apply 3 commits of en to ja
Hunk1: apply @8526500 to ja
Hunk2: apply @a8d1e03 to ja
Hunk3: apply @67bc107 to ja
Merge pull request #403 from harupong/ja-chapter7

[ja] Update chapter7 and README