Add hint for federated sharing

[MorrisJobke]

• followup to Add more hints to settings #4540
• @karlitschek proposed to not show Nextcloud in branded instances. If we do this then every single branded on (even if only the color is changed) will not show this text anymore. I guess we need to find another way to hide this. Because this is a user setting and allows the discovery of the feature.

@nickvergessen @juliushaertl @rullzer Any idea?

[mention-bot]

@MorrisJobke, thanks for your PR! By analyzing the history of the files in this pull request, we identified @schiessle, @jancborchardt and @LukasReschke to be potential reviewers.

[karlitschek]

For all other hints i avoided mentioning Nextcloud at all. So this is all o.k. This is a special case. Maybe we keep on mentioning all three products in here. It is a shares standard after all. 👍 from me

[jancborchardt]

I also think we should be specific here, as said in the original issue. Especially federated sharing needs the explanation. ;)