Update pull_request_template.md

Author: Przemog1

.github/pull_request_template.md

@@ -6,3 +6,7 @@
 
 ## TODO list:
 <!-- A list of things that have to be finished before this PR can be merged -->
+
+<!--
+By creating this pull request into Nabla, you agree to release all your past (even from previous commits) and present contributions in the Nabla repository under the Apache 2.0 license. If you're not the sole contributor, ensure that all contributors have signed the CLA agreeing to this.
+-->