doc: how to build project locally

[punndcoder28]

Hey! This is an amazing project which will make companies aware of their carbon footprint even though if they do not own their infrastructure systems. I was going through the CONTRIBUTING.md and could not find any instruction on how to build and test the project locally as I would love to contribute to the project. The table of contents does have the section Your First Code Contribution but looks like it is incomplete. Would love if I can get more information or if the file is updated. Thanks!