Added a part about the command-line tool in README (#189)

README.md

@@ -53,6 +53,22 @@ Or run [examples/masked.py][masked] to see more options. A sample output is:
 Getting fancy with some colors:
 ![Parrot with rainbow colors](examples/parrot.png)
 
+
+## Command-line usage
+
+The `wordcloud_cli.py` tool can be used to generate word clouds directly from the command-line:
+
+	$ wordcloud_cli.py --text mytext.txt --imagefile wordcloud.png
+
+If you're dealing with PDF files, then `pdftotext`, included by default with many Linux distribution, comes in handy:
+
+	$ pdftotext mydocument.pdf - | wordcloud_cli.py --imagefile wordcloud.png
+
+In the previous example, the `-` argument orders `pdftotext` to write the resulting text to stdout, which is then piped to the stdin of `wordcloud_cli.py`.
+
+Use `wordcloud_cli.py --help` so see all available options.
+
+
 ## Used in
 
 ### Reddit Cloud