chore: add PR template

Author: barmac

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,24 @@
+### Proposed Changes
+
+<!--
+Add relevant context (issue fixed or related to), a visual example
+(screenshots or short videos) of UI/UX changes if any, and steps to try out your
+changes. Ensure that any new additions or modifications are consistent with the
+existing UI and UX patterns.
+-->
+
+### Checklist
+
+Ensure you provided everything we need to review your contribution:
+
+* [ ] Your __contribution meets the [definition of done](https://github.com/bpmn-io/.github/blob/main/resources/DEFINITION_OF_DONE.md)__
+* [ ] Any new additions or modifications are __consistent with the existing UI and UX patterns__
+* [ ] __Pull request description establishes context__:
+  * [ ] __Link to related issue(s)__, i.e. `Closes {LINK_TO_ISSUE}` or `Related to {LINK_TO_ISSUE}`
+  * [ ] __Brief textual description__ of the changes
+  * [ ] __Screenshots or short videos__ showing UI/UX changes
+  * [ ] __Steps to try out__, i.e. [using the `@bpmn-io/sr` tool](https://github.com/bpmn-io/sr)
+
+<!--
+Thanks for creating this pull request! ❤️
+-->