Added periods to the end of sentences.

CONTRIBUTING.md

@@ -58,7 +58,7 @@ python -m unittest tests/*.py -v
 
 ## Testing changes to the website
 
-The [Docusaurus](https://docusaurus.io/)-based documentation website can be run by installing dependencies, then simply running `npm run start`
+The [Docusaurus](https://docusaurus.io/)-based documentation website can be run by installing dependencies, then simply running `npm run start`.
 
 ```bash
 cd website/
@@ -66,6 +66,6 @@ npm i
 npm run start
 ```
 
-The website will be available on [http://localhost:3000](http://localhost:3000)
+The website will be available on [http://localhost:3000](http://localhost:3000).
 
 Edit files in `website/` and `docs/` respectively to edit documentation.