clarify the api key

pyup/templates/_api_key.md

@@ -1,4 +1,4 @@
 {% if not api_key %}
 ---
-*Adding an API key gives you access to pyup.io's latest vulnerability database and pull requests with changelogs. [Learn More](https://pyup.io/docs/api-key/)*
+*Running the bot with an API key allows it to query pyup.io's API for changelogs and insecure packages. This is highly recommended for production use. [Learn More](https://pyup.io/docs/api-key/)*
 {% endif %}