Add note about dev_type choice to Context constructor docs

doc/runtime.rst

@@ -145,6 +145,24 @@ Platforms, Devices and Contexts
         :func:`create_some_context`. See, e.g. this
         `explanation by AMD <http://developer.amd.com/support/KnowledgeBase/Lists/KnowledgeBase/DispForm.aspx?ID=71>`_.
 
+    .. note::
+
+        Because of how OpenCL changed in order to support Installable Client
+        Drivers (ICDs) in OpenCL 1.1, the following will *look* reasonable
+        but often actually not work::
+
+            import pyopencl as cl
+            ctx = cl.Context(dev_type=cl.device_type.ALL)
+
+        Instead, make sure to choose a platform when choosing a device by type::
+
+            import pyopencl as cl
+
+            platforms = cl.get_platforms()
+            ctx = cl.Context(
+                    dev_type=cl.device_type.ALL,
+                    properties=[(cl.context_properties.PLATFORM, platforms[0])])
+
     .. note::
 
         For