[SQL][Doc] Keep Spark SQL README.md up to date

marmbrus
Update README.md to be consistent with Spark 1.1

Author: Liquan Pei <liquanpei@gmail.com>

Closes #2706 from Ishiihara/SparkSQL-readme and squashes the following commits:

33b9d4b [Liquan Pei] keep README.md up to date
[SPARK-3707] [SQL] Fix bug of type coercion in DIV

Calling `BinaryArithmetic.dataType` will throws exception until it's resolved, but in type coercion rule `Division`, seems doesn't follow this.

Author: Cheng Hao <hao.cheng@intel.com>

Closes #2559 from chenghao-intel/type_coercion and squashes the following commits:

199a85d [Cheng Hao] Simplify the divide rule
dc55218 [Cheng Hao] fix bug of type coercion in div