XEP-0472: Pubsub Social Feed, cleaner pubsub#type, discovery section

[edhelas]

• Change the pubsub#type to be consistent with other XEPs such as XEP-0372
• Add a Discovery section

[Kev]

Could you change the version to 0.2.0 to satisfy the checker, please?

[edhelas]

@Kev here we go :)

[Kev]

Ta muchly.