Add guidelines to using the new version of `UI5PathGraph`

[jeongsoolee09]

The new version of UI5PathGraph based on the latest version of DataFlow library needs some clarification on its usage:

1. We can give some background story of why this custom path graph came into being.
2. We need to clarify on why there are primary source / primary sinks and what they are used for.
3. We need to provide example instantiations of UI5PathGraph and to use that further in queries.