[Doc][FAQ] Add the doc of "how to organize DevLake project"

[Startrekzky]

Documentation Scope

• Add a FAQ folder here https://devlake.apache.org/docs/Overview/Introduction
• Add a doc of "how to organize DevLake project" to the FAQ folder

Describe the Change

The doc should answer at least the following questions:

1. What is a DevLake project?
2. As a team lead, how many DevLake projects do I need?
3. How do we organize projects when there is data from multiple connection(s)?
4. How do I know if the data of a project is successfully collected?
5. How can I observe metrics by project?