[docs] provide more docs

[celrenheit]

Although the project is moving quickly, documentation is a necessity and will be prioritized.

• Basic API docs (WIP: https://docs.sandglass.stream)
• Clients development guides
• General overview of sandglass internals
• Guides for starting a cluster

[c1tt1]

I agree, the current documentation is quite good but there should be more documentation on the service usage for example with the Homebrew installation, and also maybe a guide for developing clients.