WIP: Improve high level api docs

[sandorkertesz]

Description

At the moment the high-level and array level API is the same (the high level methods simply delegate the call to the array level). However, the high level methods are undocumented. The aim of this PR is to show the same documentation for both the high and array level methods in RTD.

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

[sandorkertesz]

Current status:

• The @add_doc_from decorator was added experimentally to the thermo.celsius_to_kelvin method.
• However, it seems that autoapi is building the documentation without importing the actual module, so the docstring does not appear in the docs.
• So far it only worked if I added the docsting to the method manually (as a string literal)