Setup a Redirect Box for Preview RST version (#122)

* test a redirrafe redirect

* try setting up an rst page

* remove redirrafe

* add external link page to project

* update front page admonition

* minor edit

* remove from toc

* add out of sight link

* update link to rst-python

Author: mmcky

lectures/intro.md

@@ -26,3 +26,7 @@ For an overview of the series, see [this page](https://quantecon.org/python-lect
 ```{tableofcontents}
 ```
 
+
+```{admonition} Previous website
+While this new site will receive all future updates, you may still view the [old site here](https://rst-python.quantecon.org) for the next month.
+```