Fix documentation build

Fix warnings that occur when building the documentation with sphinx.

Closes #105 (closed)

docs/source/about.rst

+About plotID
+==================================
+
+plotID is developed at the Institut Fluidsystemtechnik within nfdi4ing at the Technische Universität Darmstadt.
+
+Acknowledgements
+----------------
+
+The authors would like to thank the Federal Government and the Heads of Government of the Länder, as well as the Joint Science Conference (GWK), for their funding and support within the framework of the NFDI4Ing consortium. Funded by the German Research Foundation (DFG) - project number 442146713.
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