Add information about functional association

Added a line about the functional association. There is much
more about the functional association at
github.com/openbmc/docs/blob/master/code-update/ubi-code-update.md#associations
but thought it was good to add a line in the Software interface
README.

Change-Id: Ibf172d15ead248bff679eb45886a0ee182612a55
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/xyz/openbmc_project/Software/README.md b/xyz/openbmc_project/Software/README.md
index df7ffec..65c8a38 100644
--- a/xyz/openbmc_project/Software/README.md
+++ b/xyz/openbmc_project/Software/README.md
@@ -137,7 +137,8 @@
 
 List `/xyz/openbmc_project/software/`.  This list can be filtered to just
 active listing `.../software/active/` and following the `software_version`
-association to retrieve version information.
+association to retrieve version information.  To list just "functional" or
+running versions list `/xyz/openbmc_project/software/functional/`.
 
 ### Find all software versions on a managed element.