fix read/write mixup

Author: Peter Hoffmann <ph@peter-hoffmann.com>

Closes #6815 from hoffmann/patch-1 and squashes the following commits:

2abb6da [Peter Hoffmann] fix read/write mixup

docs/sql-programming-guide.md

@@ -995,11 +995,11 @@ List<String> teenagerNames = teenagers.javaRDD().map(new Function<Row, String>()
 schemaPeople # The DataFrame from the previous example.
 
 # DataFrames can be saved as Parquet files, maintaining the schema information.
-schemaPeople.read.parquet("people.parquet")
+schemaPeople.write.parquet("people.parquet")
 
 # Read in the Parquet file created above.  Parquet files are self-describing so the schema is preserved.
 # The result of loading a parquet file is also a DataFrame.
-parquetFile = sqlContext.write.parquet("people.parquet")
+parquetFile = sqlContext.read.parquet("people.parquet")
 
 # Parquet files can also be registered as tables and then used in SQL statements.
 parquetFile.registerTempTable("parquetFile");