update colab nb to be more explicit about channel selection

Author: mrariden

notebooks/run_Cellpose-SAM.ipynb

@@ -219,7 +219,13 @@
         "id": "CfhdXrkmMV2p"
       },
       "source": [
-        "Use the dropdowns below to select the _zero-indexed_ channels of your image to segment. The order does not matter. Remember to rerun the cell after you edit the dropdowns."
+        "### Channel Selection: \n",
+        "\n",
+        "- Use the dropdowns below to select the _zero-indexed_ channels of your image to segment. The order does not matter. Remember to rerun the cell after you edit the dropdowns.\n",
+        "\n",
+        "- If you have a histological image taken in brightfield, you don't need to adjust the channels.\n",
+        "\n",
+        "- If you have a fluroescent image with multiple stains, choosing multiple channels may produce segmentaiton of all the structures in the image. If you don't want to segment all the structures in the image set the channels that you don't want to be segmented to `None`, below. "
       ]
     },
     {