Merge pull request #3 from rover12421/master

Introduction 校稿 ;)
Chapter 4. Installing Gradle 校稿

1. 4.1. Prerequisites 重新翻译过,ptah位置有加译注,翻译的不太好
2. 4.3. Unpacking 最前面关于发行包的翻译,忠于原文,并添加译注
Merge pull request #4 from rover12421/master

Chapter 4. Installing Gradle 校稿