Added a note about where the greeter example comes from

Author: HChughtai

ch04packaging/04documentation.ipynb

@@ -90,7 +90,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "We're going to document our \"greeter\" example using docstrings with Sphinx.\n",
+    "We're going to document our \"greeter\" example from the previous section using docstrings with Sphinx.\n",
     "\n",
     "There are various conventions for how to write docstrings, but the native sphinx one doesn't look nice when used with\n",
     "the built in `help` system.\n",