There is no built-in functionality at the moment to add a description to an asset group. You can only specify a name for now. I've added the description feature to our customer wish list, but I cannot give a release date for it unfortunately. Theoretically, you could add a description field directly to the relevant database table (e.g. tblAssetGroups for static and dynamic groups), but this is not something we can provide instructions for. Making custom database changes is unsupported and could break your installation.