coral: update test command for CUDA-enabled hwloc

Problem: Right now the documentation instructs the user to run `lstopo |
grep -i coproc`, which is an OK test, but it is possible:

1. for the right binary to be in the user's PATH but the wrong library
to be found by ld
2. the wrong binary to be in the user's PATH but the right library be
found by ld.

The latter is the case on Lassen where the module file only updates the
LD_LIBRARY_PATH.

Solution: Have the user test the intended behavior directly with
`flux start flux resource list`.

Closes flux-framework#71

coral.rst

@@ -88,17 +88,22 @@ On all systems, Flux relies on hwloc to auto-detect the on-node resources
 available for scheduling.  The hwloc that Flux is linked against must be
 configured with ``--enable-cuda`` for Flux to be able to detect Nvidia GPUs.
 
-You can test to see if your system default hwloc is CUDA-enabled with:
+If running on an LLNL CORAL system, you can load a CUDA-enabled hwloc with:
 
 .. code-block:: sh
 
-  lstopo | grep CoProc
-
-If no output is produced, then your hwloc is not CUDA-enabled.
+  module load hwloc/1.11.10-cuda
 
-If running on an LLNL CORAL system, you can load a CUDA-enabled hwloc with:
+You can test to see if the hwloc that Flux is linked against is CUDA-enabled by
+running:
 
-.. code-block:: sh
+.. code-block:: terminal
 
-  module load hwloc/1.11.10-cuda
+  $ flux start flux resource list
+        STATE NNODES   NCORES    NGPUS
+         free      1       40        4
+    allocated      0        0        0
+         down      0        0        0
 
+If the number of free GPUs is 0, then the hwloc that Flux is linked against is
+not CUDA-enabled.