added a `permissions` example with just a per-user-throttle which we may want to…

added a `permissions` example with just a per-user-throttle which we may want to expand with some auth examples.

examples/permissionsexample/urls.py

+from django.conf.urls.defaults import patterns, url
+from permissionsexample.views import ThrottlingExampleView
+
+urlpatterns = patterns('',
+    url(r'^$',                 ThrottlingExampleView.as_view(), name='throttled-resource'),
+)

examples/permissionsexample/views.py

+from djangorestframework.views import View
+from djangorestframework.permissions import PerUserThrottling
+
+
+class ThrottlingExampleView(View):
+    """
+    A basic read-only View that has a **per-user throttle** of 10 requests per minute.
+    
+    If a user exceeds the 10 requests limit within a period of one minute, the
+    throttle will be applied until 60 seconds have passed since the first request.
+    """
+    
+    permissions = ( PerUserThrottling, )
+    throttle = '10/min'
+    
+    def get(self, request):
+        """
+        Handle GET requests.
+        """
+        return "Successful response to GET request because throttle is not yet active."
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