Emphasize object construction and management in README.md

[scheibel]

There are confusions about memory management in globjects. We should extend the README.md to reflect on the different use-cases and abstraction mechanisms globjects provides and relies on, namely: reference counting, ref_ptr, clear examples, comments on auto-resolution, ...

[cgcostume]

is this still required?

[scheibel]

Required: yes However, we don't use ref_ptr anymore so the Readme should be extended using unique_ptr, shared_ptr, weak_ptr, make_unique, and ::create patterns.