Added more information about Asset Tag

Added a more descriptive definition of "Asset Tag".
Took from http://ipmiutil.sourceforge.net/man.htm.
This change lets the user know the asset tag should be unique.
This should not change how "Asset Tag" is used.

Change-Id: Ie41cfe1e161a57ad7d08b0b1276676116b3504df
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/xyz/openbmc_project/Inventory/Decorator/AssetTag.interface.yaml b/xyz/openbmc_project/Inventory/Decorator/AssetTag.interface.yaml
index 2c674cc..3b3e047 100644
--- a/xyz/openbmc_project/Inventory/Decorator/AssetTag.interface.yaml
+++ b/xyz/openbmc_project/Inventory/Decorator/AssetTag.interface.yaml
@@ -1,5 +1,6 @@
 description: >
-    Implement to provide Asset Tag.
+    Implement to provide Asset Tag. The asset tag is used to uniquely identify
+    the object.
 properties:
     - name: AssetTag
       type: string