Merge pull request #3047 from sendgrid/ksigler7-patch-29

adding issue linking to PR template

Author: Whatthefoxsays

.github/PULL_REQUEST_TEMPLATE

@@ -13,5 +13,9 @@ Fill out this form in the body:
 **Description of the change**:
 **Reason for the change**:
 **Link to original source**:
+<!-- 
+If this pull request closes an issue, add in the issue number here 
+-->
+Closes #
 
 @ksigler7