RFR: 846: Document the need to enable Github Actions on personal forks that offer testing

[Erik Helin]

On Tue, 15 Dec 2020 15:57:55 GMT, Robin Westberg <rwestberg at openjdk.org> wrote:

> Forks created after pre-submit testing using GitHub actions was introduced need to explicitly allow GitHub actions. Post a notice as a separate check result if we detect this condition.

Looks good!

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Marked as reviewed by ehelin (Reviewer).

PR: https://git.openjdk.java.net/skara/pull/974