Use relative path for docroot

Author: stsewd

readthedocs/doc_builder/backends/mkdocs.py

@@ -81,6 +81,7 @@ def append_conf(self, **__):
         # Handle custom docs dirs
         user_docs_dir = user_config.get('docs_dir')
         docs_dir = self.docs_dir(docs_dir=user_docs_dir)
+        docs_dir = os.path.relpath(docs_dir, self.root_path)
         self.create_index(extension='md')
         user_config['docs_dir'] = docs_dir