Update README

Added a period at the end of the sentence.

Author: kseniaanske

README.md

@@ -1,6 +1,6 @@
 # Welcome to Streamlit!
 
-Edit `/streamlit_app.py` to customize this app to your heart's desire :heart:
+Edit `/streamlit_app.py` to customize this app to your heart's desire. :heart:
 
 If you have any questions, checkout our [documentation](https://docs.streamlit.io) and [community
 forums](https://discuss.streamlit.io).