Fix 404 Links in Architecture Overview (closes #653)

[tkowark]

Replaces https://github.com/corona-warn-app/cwa-app-android/pull/677/files as we only want to cherry pick the 404 fixes.

Checklist

• Test your changes as thoroughly as possible before you commit them. Preferably, automate your test by unit/integration tests.
• If this PR comes from a fork, please Allow edits from maintainers
• Set a speaking title. Format: {task_name} (closes #{issue_number}). For example: Use logger (closes # 41)
• Link your Pull Request to an issue - Pull Requests that are not linked to an issue with you as an assignee will be closed, except for minor fixes for typos or grammar mistakes in documentation or code comments.
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• Make sure that your PR does not contain changes in text files, therefore the PR must not contain changes in values/strings/* and / or assets/* (see issue [HELP WANTED][README] Text / Translations  #332 for further information)
• Make sure that your PR does not contain compiled sources (already set by the default .gitignore) and / or binary files

Description

[tkowark]

Kudos to @pr1metine

[pr1metine]

About time 😅. I already gave up on this.