https://spark-project.atlassian.net/browse/SPARK-1105
fix site scala version error
Author: CodingCat <zhunansjtu@gmail.com>
Closes#618 from CodingCat/doc_version and squashes the following commits:
39bb8aa [CodingCat] more fixes
65bedb0 [CodingCat] fix site scala version error in doc
Adds links to new instructions in:
* The main Spark project README.md
* The docs nav menu called "More"
* The docs Overview page under the "Building" and "Where to Go from Here" sections