docs: fix documentation broken links and enhance readability

[Viktordgbpcv]

Description:

This PR addresses multiple issues within the documentation of the fractal-bitcoin/fractal repository, including fixing broken links, correcting spelling errors, resolving formatting inconsistencies, and enhancing the overall readability of the documentation.

Changes Made:

1. Updated all broken links to ensure they point to the correct pages.
2. Corrected spelling errors and resolved formatting inconsistencies in the documentation.
3. Enhanced Markdown formatting and readability in src/test/README.md.
4. Improved Markdown formatting and readability in the main README document.

Testing:

• Manually verified the validity of all updated links.
• Ensured that the documentation displays correctly across different Markdown renderers.
• Reviewed the enhanced formatting to confirm improved readability.

Impact:

These changes affect only the documentation and do not impact the code or functionality.

Related Issue: #7

[proteanx]

I would think it would be better to update the documentation to actually be for fractal rather than bitcoin core... but there's been virtually no activity from the fractal team on here anyways.