doc: Broken links

Afected URL: https://canonical-microceph.readthedocs-hosted.com/en/reef-stable/
In the top left there is Canonical logo followed by the 'MicroCeph'. The link points to an empty URL:

Also in the footer of the same website there is broken link to 'Edit this page on GitHub' -> https://github.com/canonical/microceph/edit/main/docsindex.rst

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Document: index.rst

Open the documented index.rst page and compare the rendered MicroCeph logo link and footer's “Edit this page on GitHub” link with the URLs in the issue. Correct both broken links, then rebuild or preview the documentation site and verify that each link points to the intended destination.

Written by the indexing model from the issue text.