[SPARK-6806] [SPARKR] [DOCS] Add a new SparkR programming guide

This PR adds a new SparkR programming guide at the top-level. This will be useful for R users as our APIs don't directly match the Scala/Python APIs and as we need to explain SparkR without using RDDs as examples etc.

cc rxin davies pwendell

cc cafreeman -- Would be great if you could also take a look at this !

Author: Shivaram Venkataraman <shivaram@cs.berkeley.edu>

Closes #6490 from shivaram/sparkr-guide and squashes the following commits:

d5ff360 [Shivaram Venkataraman] Add a section on HiveContext, HQL queries
408dce5 [Shivaram Venkataraman] Fix link
dbb86e3 [Shivaram Venkataraman] Fix minor typo
9aff5e0 [Shivaram Venkataraman] Address comments, use dplyr-like syntax in example
d09703c [Shivaram Venkataraman] Fix default argument in read.df
ea816a1 [Shivaram Venkataraman] Add a new SparkR programming guide Also update write.df, read.df to handle defaults better

1 files changed, 1 insertions, 1 deletions

diff --git a/docs/index.md b/docs/index.md
index 5ef6d983c4..fac071da81 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -54,7 +54,7 @@ Example applications are also provided in Python. For example,
 
     ./bin/spark-submit examples/src/main/python/pi.py 10
 
-Spark also provides an experimental R API since 1.4 (only DataFrames APIs included).
+Spark also provides an experimental [R API](sparkr.html) since 1.4 (only DataFrames APIs included).
 To run Spark interactively in a R interpreter, use `bin/sparkR`:
 
     ./bin/sparkR --master local[2]