Add band index description to markdown cells (#814)

Author: tylere

docs/src/examples/notebooks/Working_with_STAC_simple.ipynb

@@ -261,7 +261,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "Apply Expression between assets"
+    "Use an expression to calculate a band index (NDVI) based on information contained in multiple assets."
    ]
   },
   {
@@ -302,6 +302,13 @@
     "m"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "If you don't use the  `asset_as_band=True` option, you need to append the band to the asset name within the expression. For example, `nir` becomes `nir_b1`."
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": null,
@@ -313,7 +320,6 @@
     "    f\"{titiler_endpoint}/stac/WebMercatorQuad/tilejson.json\",\n",
     "    params = (\n",
     "        (\"url\", stac_item),\n",
-    "        # if you don't use `asset_as_band=True` option you need to pass the band indexes within the expression\n",
     "        (\"expression\", \"(nir_b1-red_b1)/(nir_b1+red_b1)\"),  # NDVI\n",
     "        (\"rescale\", \"-1,1\"),\n",
     "        (\"minzoom\", 8),\n",