This is where you start. This is where the foundation for your success comes from.
Every successful technological company starts with a profitable business model. Every great technological company also has a clear mission in this world. The mission answers a simple yet the most important question — what the company promises to its customers? And the values are the promises to employees on what's considered as good and what's bad.
A few critical things:
Knowing these facts you need to be a master in managing highly skilled professionals and contributing to their well-being, organizing their work in a way that earns money for the company and making the right decisions in the tech field.
Although Handbook may be considered as "a guide to help employees onboard", it is an extremely important asset that will drive and guide your employees on a daily basis. If made public - it will serve as an advertising material, attracting great talent and partners. They will be able to better understand your organization and its values before shaking hands.