docs: add PULL_REQUEST_TEMPLATE.md (CirclonGroup#841)

Author: tobiasengelhardt

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,39 @@
+## PR Checklist
+Please check if your PR fulfills the following requirements:
+
+- [ ] The commit message follows our guidelines: https://github.com/CirclonGroup/angular-tree-component/blob/master/CONTRIBUTING.md#commit-message-guidelines
+- [ ] Tests for the changes have been added (for bug fixes / features)
+
+## PR Type
+What kind of change does this PR introduce?
+
+<!-- Please check the one that applies to this PR using "x". -->
+
+```
+[ ] Bugfix
+[ ] Feature
+[ ] Code style update (formatting, local variables)
+[ ] Refactoring (no functional changes, no api changes)
+[ ] Build related changes
+[ ] CI related changes
+[ ] Documentation content changes
+[ ] Other... Please describe:
+```
+
+## What is the current behavior?
+<!-- Please describe the current behavior that you are modifying, or link to a relevant issue. -->
+
+Closes #
+
+## What is the new behavior?
+
+## Does this PR introduce a breaking change?
+
+```
+[ ] Yes
+[ ] No
+```
+
+<!-- If this PR contains a breaking change, please describe the impact and migration path for existing applications below. -->
+
+## Other information