pyproject.toml: fix path of the readme file (#1201)

+ pyproject.toml: fix path of the readme file, as the 2nd attempt to fix the "Not finding README.md specified in pyprojet.toml" error on PyPI website.

pyproject.toml

@@ -108,7 +108,7 @@ include-package-data = true
 
 [tool.setuptools.dynamic]
 dependencies = { file = ["requirements.txt"] }
-readme = { file = ["README.md"], content-type = "text/markdown" }
+readme = { file = ["docs/README.md"], content-type = "text/markdown" }
 
 # extra requirements: `pip install pysolid[test]` or `pip install .[test]`
 [tool.setuptools.dynamic.optional-dependencies.test]