build: add requirements.txt file

pyproject.toml

@@ -9,6 +9,7 @@ dynamic = ["readme", "version"]
 classifiers = [
     "Programming Language :: Python :: 3",
 ]
+dependencies = ["pyaml"]
 
 [tool.setuptools.dynamic]
 readme = {file = ["README.org"], content-type = "text/plain"}

requirements.txt

+pyaml