(#1221) Add images checkbox

Added checkbox to the pull request template for any images added to the shared img repository including a checkbox to add the URL to the PR.

Author: alexaveldanez

.github/PULL_REQUEST_TEMPLATE.md

@@ -48,6 +48,8 @@ Please remove all comments before submitting.
 
 * [ ] Requires a change to menu structure (top or left-hand side)/
 * [ ] Menu structure has been updated
+* [ ] Images added to the [img](https://github.com/chocolatey/img) repository?
+    * [ ] PR -
 
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