[github] Added PR template

Author: nor3th

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,37 @@
+<!--
+Thank you very much for your pull request to the OpenCTI project! We as a community
+driven project depend on support and contributions like this!
+
+Thus already a BIG THANK YOU upfront to you for choosing to help with your PR.
+-->
+
+### Proposed changes
+
+*
+*
+
+### Related issues
+
+*
+*
+
+### Checklist
+
+<!--
+Please submit the source code in a way, where you could honestly say `This code is finished`.
+If you feel that there are possibilities for improving the code quality, please do so. 
+By doing this, you are actively helping us to improve the quality of the entire OpenCTI project.
+-->
+
+- [ ] I consider the submitted work as finished
+- [ ] I tested the code for its functionality
+- [ ] I wrote test cases for the relevant uses case
+- [ ] I added/update the relevant documentation (either on github or on notion)
+- [ ] Where necessary I refactored code to improve the overall quality
+
+<!-- _NOTE: these things are not required to open a PR and can be done afterwards / while the PR draft is open._ -->
+<!-- For completed items, change [ ] to [x]. -->
+
+### Further comments
+
+If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...