Fix markdown style for better readability

object_detection/g3doc/preparing_inputs.md

@@ -11,7 +11,7 @@ The raw 2012 PASCAL VOC data set can be downloaded
 [here](http://host.robots.ox.ac.uk/pascal/VOC/voc2012/VOCtrainval_11-May-2012.tar).
 Extract the tar file and run the `create_pascal_tf_record` script:
 
-```
+```bash
 # From tensorflow/models/object_detection
 tar -xvf VOCtrainval_11-May-2012.tar
 python create_pascal_tf_record.py --data_dir=VOCdevkit \
@@ -20,11 +20,11 @@ python create_pascal_tf_record.py --data_dir=VOCdevkit \
     --year=VOC2012 --set=val --output_path=pascal_val.record
 ```
 
-You should end up with two TFRecord files named pascal_train.record and
-pascal_val.record in the tensorflow/models/object_detection directory.
+You should end up with two TFRecord files named `pascal_train.record` and
+`pascal_val.record` in the `tensorflow/models/object_detection` directory.
 
 The label map for the PASCAL VOC data set can be found at
-data/pascal_label_map.pbtxt.
+`data/pascal_label_map.pbtxt`.
 
 ## Generation the Oxford-IIIT Pet TFRecord files.
 
@@ -32,14 +32,14 @@ The Oxford-IIIT Pet data set can be downloaded from
 [their website](http://www.robots.ox.ac.uk/~vgg/data/pets/). Extract the tar
 file and run the `create_pet_tf_record` script to generate TFRecords.
 
-```
+```bash
 # From tensorflow/models/object_detection
 tar -xvf annotations.tar.gz
 tar -xvf images.tar.gz
 python create_pet_tf_record.py --data_dir=`pwd` --output_dir=`pwd`
 ```
 
-You should end up with two TFRecord files named pet_train.record and
-pet_val.record in the tensorflow/models/object_detection directory.
+You should end up with two TFRecord files named `pet_train.record` and
+`pet_val.record` in the `tensorflow/models/object_detection` directory.
 
-The label map for the Pet dataset can be found at data/pet_label_map.pbtxt.
+The label map for the Pet dataset can be found at `data/pet_label_map.pbtxt`.