move CHECKLIST to the end

## Rationale

The github/gitter UIs show the content of a PR-link on mouse-over.

Having the CHECKLIST on top results in those pop-ups showing the checklist instead of the (more relevant) description.

.github/PULL_REQUEST_TEMPLATE.md

@@ -5,18 +5,18 @@ Please review the [guidelines for contributing](http://solidity.readthedocs.io/e
 Please also note that this project is released with a [Contributor Code of Conduct](CONDUCT.md). By participating in this project you agree to abide by its terms.
 -->
 
+### Description
+
+<!--
+Please explain the changes you made here.
+
+Thank you for your help!
+-->
+
 ### Checklist
 - [ ] Code compiles correctly
 - [ ] All tests are passing
 - [ ] New tests have been created which fail without the change (if possible)
 - [ ] README / documentation was extended, if necessary
 - [ ] Changelog entry (if change is visible to the user)
 - [ ] Used meaningful commit messages
-
-### Description
-
-<!--
-Please explain the changes you made here.
-
-Thank you for your help!
--->