Document the CLI

Add preliminary documentation for the CLI in the README.  This is pretty
sparse.  It's mostly helpful for me to remember the CLI interface as I'm
working on this project in spurts.

Addresses openelections#18
openelections#18

README.md

@@ -16,8 +16,40 @@ Clarify can be installed using pip:
 pip install clarify
 ```
 
-Usage
------
+Command line interface
+----------------------
+
+Clarify provides a command line interface for downloading jurisdictions and results from a Clarity system.
+
+### Get jurisdictions
+
+Since it can take a long time to download results for all counties in a state, Clarify has a `jurisdictions` sub-command that lists all sub-jurisdictions available from a given results URL.
+
+Running the command:
+
+    clarify jurisdictions http://results.enr.clarityelections.com/AR/63912/184685/Web01/en/summary.html
+
+Produces the output:
+
+    name,level,url
+    AR,state,http://results.enr.clarityelections.com/AR/63912/184685/Web01/en/summary.html
+    Arkansas,county,http://results.enr.clarityelections.com/AR/Arkansas/63914/184003/Web01/en/summary.html
+    Ashley,county,http://results.enr.clarityelections.com/AR/Ashley/63915/183908/Web01/en/summary.html
+    Baxter,county,http://results.enr.clarityelections.com/AR/Baxter/63916/184088/Web01/en/summary.html
+    Benton,county,http://results.enr.clarityelections.com/AR/Benton/63917/183978/Web01/en/summary.html
+    Boone,county,http://results.enr.clarityelections.com/AR/Boone/63918/183495/Web01/en/summary.html
+    Bradley,county,http://results.enr.clarityelections.com/AR/Bradley/63919/183785/Web01/en/summary.html
+    Calhoun,county,http://results.enr.clarityelections.com/AR/Calhoun/63920/184123/Web01/en/summary.html
+    Carroll,county,http://results.enr.clarityelections.com/AR/Carroll/63921/184156/Web01/en/summary.html
+
+### Get results for a jurisdiction
+
+You can get results for a particular results URL as CSV by running the `results` sub-command.
+
+    clarify results http://results.enr.clarityelections.com/AR/Yell/63988/184121/Web01/en/summary.html
+
+Python API
+----------
 
 Election results sites running Clarity software offer detailed election results at the level of the political jurisdiction (for example, a state or county) and, optionally, sub-jurisdictions beneath that (counties and/or precincts). Clarify provides methods for discovering the URLs of structured data files and for parsing the XML versions of those files into Python objects.