[SPARK-8437] [DOCS] Corrected: Using directory path without wildcard for...

[SPARK-8437] [DOCS] Corrected: Using directory path without wildcard for filename slow for large number of files with wholeTextFiles and binaryFiles

Note that 'dir/*' can be more efficient in some Hadoop FS implementations that 'dir/' (now fixed scaladoc by using HTML entity for *)

Author: Sean Owen <sowen@cloudera.com>

Closes #7126 from srowen/SPARK-8437.2 and squashes the following commits:

7bb45da [Sean Owen] Note that 'dir/*' can be more efficient in some Hadoop FS implementations that 'dir/' (now fixed scaladoc by using HTML entity for *)