Update README.md

Author: kjaymiller

README.md

@@ -9,7 +9,7 @@
 
 ### Subscribe to the Newsletter:
 
-- https://buttondown.email/python_community_news
+- https://buttondown.email/python-community-news
 
 ## Add some Content to Talk About
 You can add some things you want us to talk about by creating an [issue](https://github.com/kjaymiller/Python-Community-News/issues/new?assignees=&labels=Content&template=news-topic.md&title=%3CTITLE+OF+THE+POST%3E).