At the moment there is not convention for discussing resource's attributes in the API Blueprint. What comes close is planned Message-body Attributes Description.
But I feel what would be the real solution is what the concept of a future API Blueprint – Resource Blueprint proposes under semantic data definition (of a resource). Refer to the example resource blueprint.
So while none of the previous is implemented, if you are looking for a convention, I would suggest consider the one as proposed in resource blueprint e.g.:
# Resource [/resource]
## Attributes
+ ip (string) ... ipv4 or ipv6 address associated with the resource
+ some-other-attribute (number, optional, `42`) ... a number of something