add usage info

README.md

@@ -12,6 +12,19 @@ Linked Data can then be generated from this data via the corresponding [rules](h
 
 ## Usage
 
+The tool takes the following arguments
+
+- `-V, --version`: output the version number
+- `-e, --entity [entity]`: Choose between "anime" and "character"
+- `-s, --start [start]`: Number of start page
+- `-t, --stop [stop]`: Number of stop page
+- `-o, --output [output]`: Path to output folder (default: "")
+- `-v, --verbose`: Make the application more talkative
+- `-h, --help`: output usage information
+
+When you execute `kitsu-downloader -e anime -s 0 -t 199 -o test`,
+the first 200 pages of anime data will be downloaded and the 200 files will be put in the folder `test`.
+
 ## License
 
 2018 Between Our Worlds, [MIT License](https://github.com/betweenourworlds/kitsu-downloader/blob/master/LICENSE.md)