[webpayments] PROPOSAL: Include an extensibility section in the browser API spec with an ISSUE marker indicating WIP. (#83)

The ISSUE marker will read as follows:
>The _JSON-LD Payment Extension specification_ (linked to the document) explains how to extend the parameters used with this API using JSON-LD. 

>NOTE: The Working Group seeks feedback from the community on that specification and how well it    furthers interoperability needs in the payments ecosystem. To provide feedback, see the _status section above_ (linked to status section of spec).

* There has not been a lot of discussion within the WG about extensibility mechanisms other than the JSON-LD proposal. At this time people should focus their feedback on that proposal. If we have another one on the table at some point, we will point people to that one as well.

* The status section should include the full instructions for feedback (e.g., email, github, etc.) so we should point people to the status section for info on providing feedback.

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Reply to this email directly or view it on GitHub:
https://github.com/w3c/webpayments/issues/83