Add a clickable link to PEP 508

docs/index.rst

@@ -110,7 +110,7 @@ Other Commands
 - ``graph`` will show you a dependency graph of your installed dependencies.
 - ``shell`` will spawn a shell with the virtualenv activated. This shell can be deactivated by using ``exit``.
 - ``run`` will run a given command from the virtualenv, with any arguments forwarded (e.g. ``$ pipenv run python`` or ``$ pipenv run pip freeze``).
-- ``check`` checks for security vulnerabilities and asserts that PEP 508 requirements are being met by the current environment.
+- ``check`` checks for security vulnerabilities and asserts that `PEP 508 <https://www.python.org/dev/peps/pep-0508/>`_ requirements are being met by the current environment.
 
 
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