[news] add news to front page (#85)

Author: mmcky

lectures/intro.md

@@ -14,8 +14,19 @@ kernelspec:
 This website presents a set of advanced lectures on quantitative economic modeling, designed and written by
 [Thomas J. Sargent](http://www.tomsargent.com/) and [John Stachurski](http://johnstachurski.net/).
 
+```{admonition} News
+[QuantEcon](https://quantecon.org) is moving to the [Jupyter Book](https://jupyterbook.org/intro.html)
+build system for all of its projects. We are a founding member of the
+[Executable Books Project](https://github.com/executablebooks), an international collaboration to
+build open source tools that facilitate publishing using the Jupyter
+ecosystem. Please send feedback to [contact@quantecon.org](mailto:contact@quantecon.org)
+```
+
 For an overview of the series, see [this page](https://quantecon.org/python-lectures/)
 
 ```{tableofcontents}
 ```
 
+```{admonition} Previous website
+While this new site will receive all future updates, you may still view the [old site here](http://rst-python-advanced.quantecon.org) for the next month.
+```