Updated the description of Heading cells, which are no longer used

docs/source/examples/Notebook/What is the Jupyter Notebook.ipynb

@@ -146,7 +146,7 @@
     "\n",
     "* **Code cells:** Input and output of live code that is run in the kernel\n",
     "* **Markdown cells:** Narrative text with embedded LaTeX equations\n",
-    "* **Heading cells:** 6 levels of hierarchical organization and formatting\n",
+    "* **Heading cells:** Jupyter no longer uses special heading cells. Instead, write your headings in Markdown cells using # characters\n",
     "* **Raw cells:** Unformatted text that is included, without modification, when notebooks are converted to different formats using nbconvert\n",
     "\n",
     "Internally, notebook documents are **[JSON](https://en.wikipedia.org/wiki/JSON) data** with **binary values [base64](http://en.wikipedia.org/wiki/Base64)** encoded. This allows them to be **read and manipulated programmatically** by any programming language. Because JSON is a text format, notebook documents are version control friendly.\n",
@@ -173,9 +173,9 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.4.0"
+   "version": "3.6.6"
   }
  },
  "nbformat": 4,
- "nbformat_minor": 0
+ "nbformat_minor": 1
 }