Fix issues in index example

[ricardoV94]

Description

The homepage example was wrong, calling model instead of mmm.
Also changed instructions to use conda, which is more beginner friendly, and the latest releases are also much faster.

Related Issue

• Closes #
• Related to #

Checklist

• Checked that the pre-commit linting/style checks pass
• Included tests that prove the fix is effective or that the new feature works
• Added necessary documentation (docstrings and/or example notebooks)
• If you are a pro: each commit corresponds to a relevant logical change

Modules affected

• MMM
• CLV

Type of change

• New feature / enhancement
• Bug fix
• Documentation
• Maintenance
• Other (please specify):

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📚 Documentation preview 📚: https://pymc-marketing--470.org.readthedocs.build/en/470/