Add support for HDFS IO engine

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/fio.1 b/fio.1
index 5291126..b5ff3cc 100644
--- a/fio.1
+++ b/fio.1
@@ -612,6 +612,9 @@
 Using Glusterfs libgfapi async interface to direct access to Glusterfs volumes without
 having to go through FUSE. This ioengine defines engine specific
 options.
+.TP
+.B hdfs
+Read and write through Hadoop (HDFS)
 .RE
 .P
 .RE