Update build-open-source.md w/ missing parachains projects (#6395)

* Update build-open-source.md w/ missing parachains

* Update docs/build/build-open-source.md

Co-authored-by: Keegan | W3F <[email protected]>

* Radha's feedback

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Co-authored-by: Keegan | W3F <[email protected]>
Co-authored-by: Filippo <[email protected]>