Create pull_request_template.md

added PR template (similar to https://github.com/kubernetes/kubernetes/edit/master/.github/PULL_REQUEST_TEMPLATE.md)

Author: petersutter

.github/pull_request_template.md

@@ -0,0 +1,20 @@
+**What this PR does / why we need it**:
+
+**Which issue(s) this PR fixes**:
+Fixes #
+
+**Special notes for your reviewer**:
+
+**Release note**:
+<!--  Write your release note:
+1. Enter your release note in the below block.
+2. If no release note is required, just write "NONE" within the block.
+
+Format of block header: <category> <target_group>
+Possible values:
+- category:       improvement|noteworthy
+- target_group:   user|operator
+-->
+```improvement operator
+
+```