Fix readme

Author: felix-zenk

pyproject.toml

@@ -5,7 +5,7 @@ build-backend = "setuptools.build_meta"
 [project]
 name = "onboardapis"
 description = "A pure Python wrapper for the on-board APIs of many different transportation providers"
-readme = {file = ["README.md"], content-type = "text/markdown"}
+readme = {file = "README.md", content-type = "text/markdown"}
 requires-python = ">=3.7"
 keywords = ["api", "train"]
 license = { text="MIT" }