docs: point to "firebase.google" domain for hyperlinks in the usage section of README.md files

[nilsreichardt]

Description

As described in #8613 are linking all README.md to the archived docs. We should change this because the docs are archived and it makes the impression that the packages are not maintained anymore, when you are linking to archived docs.

This is one of the two proposals for fixing this issue (other proposal: #8813). In this proposal, we just link to the first article of the docs.

Advantages:

• Fit into the existing style of the README.md files
• No maintaining (in comparison to docs: new format for the "Usage" section in the README.md files (proposal #1) #8813)

Disadvantages:

• The links are sometimes a bit random because the format doesn't fit anymore. For the old docs we had in most cases a "Usage". But now we have a lot of small pages.

This PR is a proposal and should show a proof of concept for the new format. If this is a good solution, I will continue adding the links for the other packages.

Related Issues

Closes #8613

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Breaking Change

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[nilsreichardt]

@russellwheatley Any thoughts on this proposal?