Add even more context about raw.githubusercontent.com domain

CONTRIBUTING.md

@@ -15,7 +15,7 @@ Submit [a Pull Request (PR)](https://github.com/adamziel/blueprints/pulls) with
 The PR should contain:
 
 * A single `blueprint.json` file under the path `blueprints/your-blueprint-name/blueprint.json` (like [the examples here](https://github.com/adamziel/blueprints/tree/trunk/blueprints)).
-* All the static files (WXR, ZIP, JPG, etc.) your Blueprint references. The static files must be loaded via the `https://raw.githubusercontent.com` URL pointing to your branch.
+* All the static files (WXR, ZIP, JPG, etc.) your Blueprint references. The static files must be loaded via the `https://raw.githubusercontent.com` URL pointing to your branch. `raw.githubusercontent.com` is a service that allows you to serve files directly from your GitHub repository. This is useful for loading static files in Blueprints. The URLs follow the `raw.githubusercontent.com/${user}/${repo}/${branch}/${path}` pattern.
 
 For example, if you want to load `a content-export.xml` file and your branch is called `woocommerce-subscriptions`, then your PR must contain a: