Update template to have user check box that doxygen is

complete.

Fixes ufs-community#1025.

.github/PULL_REQUEST_TEMPLATE

@@ -35,6 +35,10 @@ Add any links to pending PRs that are required prior to merging this PR. For exa
 ufs-community/UFS_UTILS/pull/<pr_number>
 
 ## DOCUMENTATION:
+All new and updated source code must be documented with Doxygen.
+
+- [ ] Doxygen is updated.
+
 If this PR is contributing new capabilities that need to be documented, please also include updates to the RST files in the docs/source directory as supporting material.
 
 ## ISSUE: