Document additional packages needed in ubuntu

[RubenGarcia]

First time contributor checklist:

• [ X] I have read the README and Contributor Guidelines

Contributor checklist:

• [X ] My commits are in nice logical chunks with good commit messages
• [ X] My changes are rebased on the latest clearnet branch
• [X ] A yarn ready run passes successfully (more about tests here)
• [X ] My changes are ready to be shipped to users

Description

I followed the instructions on the CONTRIBUTING file on a new Ubuntu machine.

yarn build-everything

was failing on cmake-js, so I installed it. I also installed cmake, as that is required for cmake-js. After doing that, yarn build-everything now works correctly. I added the needed install lines to CONTRIBUTING in this patch. Please merge.

[Bilb]

merged as part of https://github.com/oxen-io/session-desktop/pull/2917