[SPARK-8554] Add the SparkR document files to .rat-excludes for ./dev/check-license

[[SPARK-8554] Add the SparkR document files to `.rat-excludes` for `./dev/check-license` - ASF JIRA](https://issues.apache.org/jira/browse/SPARK-8554)

Author: Yu ISHIKAWA <[email protected]>

Closes #6947 from yu-iskw/SPARK-8554 and squashes the following commits:

5ca240c [Yu ISHIKAWA] [SPARK-8554] Add the SparkR document files to `.rat-excludes` for `./dev/check-license`

Author: yu-iskw

.rat-excludes

@@ -86,4 +86,8 @@ local-1430917381535_2
 DESCRIPTION
 NAMESPACE
 test_support/*
+.*Rd
+help/*
+html/*
+INDEX
 .lintr