docs: added missing execution of `melos bootstrap` in getting started file

[PrimaryFeather]

Description

While the Getting Started document tells the user about the importance of bootstrapping, the actual melos bootstrap command is neither shown nor executed. This is not a major problem, but I tripped over it while following the instructions, so I suspect it may irritate others as well.

Thus, I made that small addition.

refs #565

Type of Change

• [ ] ✨ feat -- New feature (non-breaking change which adds functionality)
• [ ] 🛠️ fix -- Bug fix (non-breaking change which fixes an issue)
• [ ] ❌ ! -- Breaking change (fix or feature that would cause existing functionality to change)
• [ ] 🧹 refactor -- Code refactor
• [] ✅ ci -- Build configuration change
• [x] 📝 docs -- Documentation
• [ ] 🗑️ chore -- Chore

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melos.invertase.dev/~615

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[PrimaryFeather]

Thanks a lot for accepting the pull request, guys! Keep up the great work with Melos! 😃