Add two approval requirement to PR template checklist (#1318)

* Add two approval requirement to PR template checklist

Signed-off-by: Grant Linville <[email protected]>

Author: g-linville

.github/PULL_REQUEST_TEMPLATE.md

@@ -5,4 +5,5 @@
 - [ ] Commits follow [contributing guidance](https://github.com/acorn-io/acorn/blob/main/CONTRIBUTING.md#commits)
 - [ ] Automated tests added to cover the changes. If tests couldn't be added, an explanation is provided in the Verification and Testing section
 - [ ] Changes to user-facing functionality, API, CLI, and upgrade impacts are clearly called out in PR description
+- [ ] PR has at least two approvals before merging (or a reasonable exception, like it's just a docs change)