📝 Add notebook comment

Author: jemrobinson

notebooks/degrid_and_visualise.ipynb

@@ -12,6 +12,8 @@
    "metadata": {},
    "source": [
     "This notebook shows how to synthetically generate non-gridded data from gridded data.\n",
+    "**You will need the gridded data, which you can download with the `extract_anomalies.ipynb` notebook, before running this notebook.**\n",
+    "\n",
     "We'll simulate two general types of non-gridded data:\n",
     "1) *Stations*, which will simply involve extracting N random points in the continuous lat-lon space covered by the grid and interpolating their values based on the surrounding gridded data, for the whole period of interest\n",
     "2) *Buoys*, which will instead involve not only extracting N random points and their values, but also N nearest neighbours in subsequent time steps, adding jitter to simulate irregularity in the movement.\n",