Documentation: Add note on shared context

Change-Id: Iddecaf7c9c8f10c84a4f5cceeb7554d266a1e94c
Signed-off-by: Cetnerowski, Adam <adam.cetnerowski@intel.com>

Author: AdamCetnerowski

documentation/LIMITATIONS.md

@@ -34,6 +34,7 @@ _Currently no plan to implement. If interested in these features, please use SRB
 #### Other capabilities
 * OpenGL sharing with MESA driver - _will implement in the future (no specific timeline)_
 * CL_MEM_SVM_FINE_GRAIN_BUFFER (if using unpatched i915) - _patch is WIP_
+* Creation of OpenCL context spanning both CPU and GPU devices is currently not supported
 
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