Update index.rst to link to Libera.Chat

[debbie-nguyen]

Update documentation to link to Libera.Chat for IRC support

Changed the reference to Libera.Chat in the documentation to a hyperlink pointing to https://libera.chat/ for better accessibility

Description

Fixes #X.

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To Do

• [ ] Documentation. (If you've added a new command-line flag, for example, find the appropriate page under docs/ to describe it.)
• [ ] Changelog. (Add an entry to docs/changelog.rst to the bottom of one of the lists near the top of the document.)
• [ ] Tests. (Very much encouraged but not strictly required.)