README.md: add Thumbnail300KURL column to images.csv. Fixes #10.

In this update, an optional Thumbnail300KURL column was added that points to a thumbnail with ~300K pixels (~640x480).

README.md

@@ -10,7 +10,7 @@ The images are listed as having a [CC BY 2.0](https://creativecommons.org/licens
 
 ## Download the data
 
-* [Image URLs and metadata](https://storage.googleapis.com/openimages/2016_08/images_2016_08_v4.tar.gz) (880 MB) -- **updated**: added OriginalSize and OriginalMD5 columns.
+* [Image URLs and metadata](https://storage.googleapis.com/openimages/2016_08/images_2016_08_v5.tar.gz) (990 MB) -- **updated**: added OriginalSize and OriginalMD5 and Thumbnail300KURL columns.
 * [Machine image-level annotations (train and validation sets)](https://storage.googleapis.com/openimages/2016_08/machine_ann_2016_08_v3.tar.gz) (450 MB)
 * [Human image-level annotations (validation set)](https://storage.googleapis.com/openimages/2016_08/human_ann_2016_08_v3.tar.gz) (9 MB)
 
@@ -31,17 +31,22 @@ The data tarballs contain CSV files of two types:
 There's one such file for each subset inside train and validation subdirectories. It has image URLs, their OpenImages IDs, titles, authors and license information:
 
 ```
-ImageID,Subset,OriginalURL,OriginalLandingURL,License,AuthorProfileURL,Author,Title,OriginalSize,OriginalMD5
+ImageID,Subset,OriginalURL,OriginalLandingURL,License,AuthorProfileURL,Author,Title,\
+OriginalSize,OriginalMD5,Thumbnail300KURL
 ...
 
 000060e3121c7305,train,https://c1.staticflickr.com/5/4129/5215831864_46f356962f_o.jpg,\
 https://www.flickr.com/photos/brokentaco/5215831864,\
 https://creativecommons.org/licenses/by/2.0/,\
 "https://www.flickr.com/people/brokentaco/","David","28 Nov 2010 Our new house."\
-211079,0Sad+xMj2ttXM1U8meEJ0A==
+211079,0Sad+xMj2ttXM1U8meEJ0A==,https://c1.staticflickr.com/5/4129/5215831864_ee4e8c6535_z.jpg
 ```
 
-The data is as it appears on the destination websites. OriginalMD5 is base64-encoded binary MD5, as described [here](https://cloud.google.com/storage/transfer/create-url-list#md5).
+The data is as it appears on the destination websites.
+
+* OriginalSize is the download size of the original image.
+* OriginalMD5 is base64-encoded binary MD5, as described [here](https://cloud.google.com/storage/transfer/create-url-list#md5).
+* Thumbnail300KURL is an optional URL to a thumbnail with ~300K pixels (~640x480). It's provided for the convenience of downloading the data in the absence of more convenient ways to get the images. If missing, the OriginalURL must be used (and then resized to the same size, if needed)
 
 ### labels.csv