Updated README to include ArchLinux support

The name from os_family was used

README.rst

@@ -17,4 +17,4 @@ Installs the chrony package.
 
 ``chrony.config``
 -----------------
-This state manages the file ``chrony.conf`` under ``/etc`` (template found in "chrony/files"). The configuration is populated by values in "chrony/map.jinja", which are based on the package's default values (for RedHat and Debian family distributions), and are overridden by values of the same name in pillar.
+This state manages the file ``chrony.conf`` under ``/etc`` (template found in "chrony/files"). The configuration is populated by values in "chrony/map.jinja", which are based on the package's default values (for RedHat, Debian and Arch family distributions), and are overridden by values of the same name in pillar.