Updated docs and README.md

[JulStraus]

I just realized that we still had some parts in it related to the non-registered version. This was adjusted in this PR.

In addition, I decided to be clearer regarding the test cases, i.e., what they test and what not.

[JulStraus]

These fails in the tests are interesting as I have not really done any changes to these checks.

I will investigate it and come back to you.

[JulStraus]

The problem is in the changes of PR #43 of EMG. The current implemented changes do not work as we return a single ExtensionData, i.e., the reference to the supertype. So I would honestly prefer to fix it within EMG.

[JulStraus]

The problem stems from changes in the ExtensionData design introduced in EnergyModelsBase v0.9.1 and the corresponding adjustment in EnergyModelsGeography v0.11.3.

I deactivated the tests in this version now as we want to get a good approach in these packages. These changes can take time to develop.

[lfbernardino]

Your changes look mostly ok, I just made some typo fixes on top of your commits.

I suggest that you create an issue within EMC, such that we don't forget to reactivate the tests once the behavior is fixed within EnergyModelsBase and EnergyModelsGeography.