add note (#69)

Author: e-marshall

book/sentinel1/nbs/4_read_pc_data.ipynb

@@ -596,7 +596,11 @@
    "id": "5178ff37-5984-4e64-beaf-03f635db087a",
    "metadata": {},
    "source": [
-    "Next, let's take a look at how backscatter values vary seasonally. To do this we will use Xarray's [groupby()](https://docs.xarray.dev/en/stable/generated/xarray.DataArray.groupby.html) and [.facetgrid](https://docs.xarray.dev/en/latest/generated/xarray.plot.FacetGrid.html) methods. We'll do this for the VV polarization:"
+    "Next, let's take a look at how backscatter values vary seasonally. To do this we will use Xarray's [groupby()](https://docs.xarray.dev/en/stable/generated/xarray.DataArray.groupby.html) and [.facetgrid](https://docs.xarray.dev/en/latest/generated/xarray.plot.FacetGrid.html) methods. We'll do this for the VV polarization. \n",
+    "\n",
+    ":::{note}\n",
+    "This section may not work on machines with less than 8GB RAM. \n",
+    ":::"
    ]
   },
   {