Fix variable redeclaration in url.origin code example (mdn#40529)

* Update index.md

* Update index.md

* Update files/en-us/web/api/url/origin/index.md

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

* Update files/en-us/web/api/url/origin/index.md

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

* add prose for examples

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Dipika Bhattacharya <dipika@foss-community.org>

Author: 3 people

files/en-us/web/api/url/origin/index.md

@@ -24,13 +24,19 @@ A string.
 
 ## Examples
 
+The following examples show how the `origin` property is computed for a `blob:` URL, an `http:` URL, and one using a non-default port:
+
 ```js
 const url = new URL("blob:https://mozilla.org:443/");
 console.log(url.origin); // 'https://mozilla.org'
+```
 
+```js
 const url = new URL("http://localhost:80/");
 console.log(url.origin); // 'http://localhost'
+```
 
+```js
 const url = new URL("https://mozilla.org:8080/");
 console.log(url.origin); // 'https://mozilla.org:8080'
 ```