[SPARK-16557][SQL] Remove stale doc in sql/README.md

## What changes were proposed in this pull request?
Most of the documentation in https://github.com/apache/spark/blob/master/sql/README.md is stale. It would be useful to keep the list of projects to explain what's going on, and everything else should be removed.

## How was this patch tested?
N/A

Author: Reynold Xin <[email protected]>

Closes #14211 from rxin/SPARK-16557.

Author: rxin

sql/README.md

@@ -1,83 +1,10 @@
 Spark SQL
 =========
 
-This module provides support for executing relational queries expressed in either SQL or a LINQ-like Scala DSL.
+This module provides support for executing relational queries expressed in either SQL or the DataFrame/Dataset API.
 
 Spark SQL is broken up into four subprojects:
  - Catalyst (sql/catalyst) - An implementation-agnostic framework for manipulating trees of relational operators and expressions.
  - Execution (sql/core) - A query planner / execution engine for translating Catalyst's logical query plans into Spark RDDs.  This component also includes a new public interface, SQLContext, that allows users to execute SQL or LINQ statements against existing RDDs and Parquet files.
  - Hive Support (sql/hive) - Includes an extension of SQLContext called HiveContext that allows users to write queries using a subset of HiveQL and access data from a Hive Metastore using Hive SerDes.  There are also wrappers that allows users to run queries that include Hive UDFs, UDAFs, and UDTFs.
  - HiveServer and CLI support (sql/hive-thriftserver) - Includes support for the SQL CLI (bin/spark-sql) and a HiveServer2 (for JDBC/ODBC) compatible server.
-
-
-Other dependencies for developers
----------------------------------
-In order to create new hive test cases (i.e. a test suite based on `HiveComparisonTest`),
-you will need to setup your development environment based on the following instructions.
-
-If you are working with Hive 0.12.0, you will need to set several environmental variables as follows.
-
-```
-export HIVE_HOME="<path to>/hive/build/dist"
-export HIVE_DEV_HOME="<path to>/hive/"
-export HADOOP_HOME="<path to>/hadoop"
-```
-
-If you are working with Hive 0.13.1, the following steps are needed:
-
-1. Download Hive's [0.13.1](https://archive.apache.org/dist/hive/hive-0.13.1) and set `HIVE_HOME` with `export HIVE_HOME="<path to hive>"`. Please do not set `HIVE_DEV_HOME` (See [SPARK-4119](https://issues.apache.org/jira/browse/SPARK-4119)).
-2. Set `HADOOP_HOME` with `export HADOOP_HOME="<path to hadoop>"`
-3. Download all Hive 0.13.1a jars (Hive jars actually used by Spark) from [here](http://mvnrepository.com/artifact/org.spark-project.hive) and replace corresponding original 0.13.1 jars in `$HIVE_HOME/lib`.
-4. Download [Kryo 2.21 jar](http://mvnrepository.com/artifact/com.esotericsoftware.kryo/kryo/2.21) (Note: 2.22 jar does not work) and [Javolution 5.5.1 jar](http://mvnrepository.com/artifact/javolution/javolution/5.5.1) to `$HIVE_HOME/lib`.
-5. This step is optional. But, when generating golden answer files, if a Hive query fails and you find that Hive tries to talk to HDFS or you find weird runtime NPEs, set the following in your test suite...
-
-```
-val testTempDir = Utils.createTempDir()
-// We have to use kryo to let Hive correctly serialize some plans.
-sql("set hive.plan.serialization.format=kryo")
-// Explicitly set fs to local fs.
-sql(s"set fs.default.name=file://$testTempDir/")
-// Ask Hive to run jobs in-process as a single map and reduce task.
-sql("set mapred.job.tracker=local")
-```
-
-Using the console
-=================
-An interactive scala console can be invoked by running `build/sbt hive/console`.
-From here you can execute queries with HiveQl and manipulate DataFrame by using DSL.
-
-```scala
-$ build/sbt hive/console
-
-[info] Starting scala interpreter...
-import org.apache.spark.sql.catalyst.analysis._
-import org.apache.spark.sql.catalyst.dsl._
-import org.apache.spark.sql.catalyst.errors._
-import org.apache.spark.sql.catalyst.expressions._
-import org.apache.spark.sql.catalyst.plans.logical._
-import org.apache.spark.sql.catalyst.rules._
-import org.apache.spark.sql.catalyst.util._
-import org.apache.spark.sql.execution
-import org.apache.spark.sql.functions._
-import org.apache.spark.sql.hive._
-import org.apache.spark.sql.hive.test.TestHive._
-import org.apache.spark.sql.hive.test.TestHive.implicits._
-import org.apache.spark.sql.types._
-Type in expressions to have them evaluated.
-Type :help for more information.
-
-scala> val query = sql("SELECT * FROM (SELECT * FROM src) a")
-query: org.apache.spark.sql.DataFrame = [key: int, value: string]
-```
-
-Query results are `DataFrames` and can be operated as such.
-```
-scala> query.collect()
-res0: Array[org.apache.spark.sql.Row] = Array([238,val_238], [86,val_86], [311,val_311], [27,val_27]...
-```
-
-You can also build further queries on top of these `DataFrames` using the query DSL.
-```
-scala> query.where(query("key") > 30).select(avg(query("key"))).collect()
-res1: Array[org.apache.spark.sql.Row] = Array([274.79025423728814])
-```