minor improvements in RTD

[SabineHaas]

Fix #Issue

Changes proposed in this pull request:

• Add two sections to entry in code documentation, that were displayed on a minor level before.
• Renamed "GRECO Results" section in RTD to "Selected results of the GRECO project"
• Minor fixes, changes, typo corrections

The following steps were realized, as well (required):

• Update the CHANGELOG.md
• Check if full simulation tests pass locally (EXECUTE_TESTS_ON=master pytest)

Also the following steps were realized (if applies):

• Use in-line comments to explain your code
• Write docstrings to your code
• For new functionalities: Explain in readthedocs
• Write test(s) for your new patch of code

Please mark above checkboxes as following:

• Open
• Done

In case of an error due to linting, run black . --exclude docs/ and push your changes.
Note that in case you do not fix a whole issue you should start your PR with Address #xyz.

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