Fix link formatting and clarify the distinction between Manim versions in index.rst

[irvanalhaq9]

Overview: What does this pull request change?

This pull request fixes the formatting of the links. Additionally, it clarifies the distinction between Manim versions, highlighting the difference between ManimCE and the original Manim.

Before

After

Motivation and Explanation: Why and how do your changes improve the library?

Reviewer Checklist

• The PR title is descriptive enough for the changelog, and the PR is labeled correctly
• If applicable: newly added non-private functions and classes have a docstring including a short summary and a PARAMETERS section
• If applicable: newly added functions and classes are tested

[behackl]

My bad, I must have missed that the recent change has introduced a markdown-link to our .rst index.

Long-term, I'd like to migrate most .rst files to .md ones (which Sphinx can parse thanks to the MyST parser anyways, but the contribution barrier is much lower with markdown than with rest).

In any case, thanks for fixing this!

[JasonGrace2282]

Long-term, I'd like to migrate most .rst files to .md ones (which Sphinx can parse thanks to the MyST parser anyways, but the contribution barrier is much lower with markdown than with rest).

Helpful link: https://docs.readthedocs.io/en/stable/guides/migrate-rest-myst.html#how-to-convert-existing-restructuredtext-documentation-to-myst
Haven't tested it on any project, but it should hopefully take care of most of the brute force work