add markdown lint (#113)

fix #112

Reviewed-on: https://gitea.com/gitea/awesome-gitea/pulls/113
Reviewed-by: techknowlogick <techknowlogick@noreply.gitea.io>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-committed-by: Lunny Xiao <xiaolunwen@gmail.com>

contributing.md

@@ -1,4 +1,5 @@
 # Contribution Guidelines
+
 - **To add, remove, or change things on the list:** Submit a pull request
 - List items should be sorted *alphabetically*.
 - Each item should be limited to one link and a description.