Document the "-m plop.collector" functionality.

Document how to use "python -m plop.collector".

Also, specify how to write out collector.stack_counts.

README.rst

@@ -28,9 +28,17 @@ Usage
 -----
 
 In the application to be profiled, create a ``plop.collector.Collector``,
-call ``start()``, wait, then ``stop()``.  Dump ``collector.stack_counts``
-to a file.  See ``ProfileHandler`` in ``demo/busy_server.py`` for an example
-of how to trigger profiling via an HTTP interface.
+call ``start()``, wait, then ``stop()``.  Write
+``repr(dict(collector.stack_counts))`` to a file.  See ``ProfileHandler`` in
+``demo/busy_server.py`` for an example of how to trigger profiling via an HTTP
+interface.
+
+To profile an entire Python script, run::
+
+    python -m plop.collector myscript.py
+
+This will write the profile to ``/tmp/plop.out``
+
 
 To use the viewer, run::