community: add pull-request template

.github/pull_request_template.md

@@ -0,0 +1,24 @@
+<!-- 
+Hi there, have an early THANK YOU for your contribution!
+k3d is a community-driven project, so we really highly appreciate any support.
+Please make sure, you've read our Code of Conduct and the Contributing Guidelines :)
+- Code of Conduct: https://github.com/rancher/k3d/blob/main/CODE_OF_CONDUCT.md
+- Contributing Guidelines: https://github.com/rancher/k3d/blob/main/CONTRIBUTING.md
+-->
+
+# What
+
+<!-- What does this PR do or change? -->
+
+# Why
+
+<!-- Link issues, discussions, etc. or just explain why you're creating this PR -->
+
+# Implications
+
+<!--
+Does this change existing behavior? If so, does it affect the CLI (cmd/) only or does it also/only change some internals of the Go module (pkg/)?
+Especially mention breaking changes here!
+-->
+
+<!-- Get recognized using our all-contributors bot: https://github.com/rancher/k3d/blob/main/CONTRIBUTING.md#get-recognized -->