pyproject: README.rst -> README.md

Author: amorison

pyproject.toml

@@ -6,7 +6,7 @@ build-backend = "setuptools.build_meta"
 name = "stagpy"
 dynamic = ["version"]
 description = "Tool for StagYY output files processing"
-readme = "README.rst"
+readme = "README.md"
 authors = [
     {name = "Adrien Morison", email = "[email protected]"},
     {name = "Martina Ulvrova"},