RFR: Improve the help for reviewers

[Erik Joelsson]

On Thu, 25 Mar 2021 00:58:54 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

> Rename "Download" to "Reviewing". Add information on how to get the PR using Skara tools and diff files. Collapse all information by default to make it more compact.
> 
> An example on how this will look can be found here: https://github.com/magicus/openjdk-sandbox/issues/1

Marked as reviewed by erikj (Reviewer).

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PR: https://git.openjdk.java.net/skara/pull/1094