added mailing list CTA (#735)

* added mailing list CTA

* added mailto: link to simplify subscribing to mailing list

* fixed missing bracket in mailing list hyperlink

---------

Co-authored-by: Matt Haigh <matthaigh@google.com>

Author: mlhaigh

README.md

@@ -166,6 +166,8 @@ Please [report the bug in VM-Packages](https://github.com/mandiant/VM-Packages/i
 Note that package updates are best effort and that updates are not being tested.
 If you encounter errors, perform a fresh FLARE-VM install.
 
+### Mailing List
+Subscribe to the FLARE mailing list for community announcements! Email "subscribe" to [flare-external@google.com](mailto:flare-external@google.com?subject=subscribe).
+
 ## Legal Notice
 > This download configuration script is provided to assist cyber security analysts in creating handy and versatile toolboxes for malware analysis environments. It provides a convenient interface for them to obtain a useful set of analysis tools directly from their original sources. Installation and use of this script is subject to the Apache 2.0 License. You as a user of this script must review, accept and comply with the license terms of each downloaded/installed package. By proceeding with the installation, you are accepting the license terms of each package, and acknowledging that your use of each package will be subject to its respective license terms.
-