Fix typos in lib/datasets/data/README.md

Summary:
Fix typos when creating symlinks for PASCAL VOC.
Closes https://github.com/facebookresearch/Detectron/pull/275

Reviewed By: rbgirshick

Differential Revision: D7274459

Pulled By: ir413

fbshipit-source-id: 8a60516ac199371f67117b29f1ebe3199dabe550

lib/datasets/data/README.md

@@ -61,8 +61,8 @@ Create symlinks for `VOC<year>`:
 ```
 mkdir -p $DETECTRON/lib/datasets/data/VOC<year>
 ln -s /path/to/VOC<year>/JPEGImages $DETECTRON/lib/datasets/data/VOC<year>/JPEGImages
-ln -s /path/to/VOC<year>/json/annotations $DETECTRON/lib/datasets/data/VOC<year>annotations
-ln -s /path/to/VOC<year>/devkit $DETECTRON/lib/datasets/VOC<year>/VOCdevkit<year>
+ln -s /path/to/VOC<year>/json/annotations $DETECTRON/lib/datasets/data/VOC<year>/annotations
+ln -s /path/to/VOC<year>/devkit $DETECTRON/lib/datasets/data/VOC<year>/VOCdevkit<year>
 ```
 
 ### PASCAL VOC Annotations in COCO Format