Add Documentation url

Show documentation URL on pypi

Author: koutoftimer

setup.py

@@ -9,6 +9,9 @@
     author="Scrapy project",
     author_email="[email protected]",
     url="https://github.com/scrapy/w3lib",
+    project_urls=[
+        "Documentation": "https://w3lib.readthedocs.io/en/latest/",
+    ],
     packages=find_packages(exclude=("tests", "tests.*")),
     package_data={
         "w3lib": ["py.typed"],