Document Support for CiviCRM from payment processors

Document appropriately the support that CiviCRM receives from a variety of payment processors.

• Payment processing feature page that cites the sponsoring payment processors
• Individual payment processor pages similar to partner detail pages
• Update the extension readme.md on extensions in gitlab
• Update extension pages on c.o (for as long as these will exist)

Josh has started on first two tasks as of Feb 22, 2021.

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Original description

Document appropriately (after determining what that means ;) ) the support that CiviCRM receives from a variety of payment processors.

This might mean putting something into the info.xml or README.md of each extension, as well as adding something somewhere on c.o.

See https://github.com/agileware/cf-stripe/issues/1

@mattwire any sense of Stripe's compensation arrangements being different in Australia compared to other countries? I like the policy thrust of @justinfreeman 's comment but don't believe it is industry practice.