[DLMED] enhance doc (#339)

Signed-off-by: Nic Ma <nma@nvidia.com>

Author: Nic-Ma

acceleration/fast_training_tutorial.ipynb

@@ -24,7 +24,7 @@
     "\n",
     "It's modified from the Spleen 3D segmentation tutorial notebook, the Spleen dataset can be downloaded from http://medicaldecathlon.com/.\n",
     "\n",
-    "[![Open In Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/Project-MONAI/tutorials/blob/master/acceleration/fast_training_tutorial.ipynb)"
+    "[![Open In Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/Project-MONAI/tutorials/blob/master/acceleration/fast_training_tutorial.ipynb)(* please note that the free GPU resource in Colab may be not as powerful as the V100 test results in this notebook: it may not support AMP and the GPU computation of transforms may be not faster than the CPU computation.)"
    ]
   },
   {
@@ -798,7 +798,7 @@
  ],
  "metadata": {
   "kernelspec": {
-   "display_name": "Python 3",
+   "display_name": "Python 3 (ipykernel)",
    "language": "python",
    "name": "python3"
   },