Reindent and add docstring

_pytest/config.py

@@ -999,6 +999,11 @@ class Config(object):
         self._warn_about_missing_assertion(mode)
 
     def _mark_plugins_for_rewrite(self, hook):
+        """
+        Given an importhook, mark for rewrite any top-level
+        modules or packages in the distribution package for
+        all pytest plugins.
+        """
         import pkg_resources
         self.pluginmanager.rewrite_hook = hook
         for entrypoint in pkg_resources.iter_entry_points('pytest11'):