The translations docs could mention the demo instance

[gonzalo-bulnes]

Describe the change

As far as I understand a demo instance is maintained up-to-date with the release candidate (https://demo.securedrop.org). That demo instance seems like a very good place for translators to get more context about translatable strings in a dynamic environment, and seems like a good complement to the screenshots that are provided in Weblate.

How will this impact users?

If more translators were aware of the availability of the demo instance, more of them could integrate it into their workflows. It may not be useful to everyone, but it seems it would be useful to some people.

User Research Evidence

Admittedly incidental evidence: I recently learnt about the demo instance when talking with @eloquence about translations context, and it was recently mentioned in Gitter in relation to translations. That makes me think a mention in the docs could be useful.

Additional context

I don't think this is urgent, and a reorganization of the translation docs is in progress, but I think of this issue as a reminder to add the mention as soon as the first iteration of the reorganization is done.