docs(contribute): adds table of contents and info about dependencies. (…

…#842)

- [x] Adds Table of Contents.
- [x] Adds a section about dependencies. 

**What kind of change does this PR introduce?**
Docs

**Motivation**
- It was getting harder to reach the desired section in the doc.
- CI failing while modifying dependency (not committing the `package-lock.json`)

Hence everything sorted  🎉