[docs] [testing] gpu decorators table (huggingface#8422)

* gpu decorators table

* whitespace

* Update docs/source/testing.rst

Co-authored-by: Lysandre Debut <lysandre@huggingface.co>

* whitespace

Co-authored-by: Lysandre Debut <lysandre@huggingface.co>

docs/source/testing.rst

@@ -409,6 +409,22 @@ decorators are used to set the requirements of tests CPU/GPU/TPU-wise:
 * ``require_torch_non_multigpu`` - as ``require_torch`` plus requires 0 or 1 GPUs
 * ``require_torch_tpu`` - as ``require_torch`` plus requires at least 1 TPU
 
+Let's depict the GPU requirements in the following table:
+
+
++----------+---------------------------------+
+| n gpus   |  decorator                      |
++==========+=================================+
+| ``>= 0`` | ``@require_torch``              |
++----------+---------------------------------+
+| ``>= 1`` | ``@require_torch_gpu``          |
++----------+---------------------------------+
+| ``>= 2`` | ``@require_torch_multigpu``     |
++----------+---------------------------------+
+| ``< 2``  | ``@require_torch_non_multigpu`` |
++----------+---------------------------------+
+
+
 For example, here is a test that must be run only when there are 2 or more GPUs available and pytorch is installed:
 
 .. code-block:: python