docs: Remove topics list from the "How to Contribute to Open Source" section

[Ayu Adiati]

Description

The "How to Contribute to Open Source" section has a list of topics that contain the titles of the sections and subsections. But we don't need this because we have a sidebar that holds these titles and serves as a Table of Contents.

Propose Solution

Remove the list in the How to Contribute to Open Source section.

Codeblocks

intro/05-how-to-contribute-to-open-source.md

Lines 3 to 8 in b4c5308

 In this chapter, we'll guide you through the process of contributing to open source projects. We'll cover the following topics: 
  
 - Finding projects to work on 
 - How to submit a contribution 
 - Onboarding in a new project 
 - What happens next? 

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Originally posted by @adiati98 in #100 (comment)

[Kedgard Cordero]

Hi @adiati98, may I be assigned to this issue?

[Ayu Adiati]

@Kenny4297 it's yours!