Update issue templates (#71)

.github/ISSUE_TEMPLATE/user-story.md

@@ -0,0 +1,24 @@
+---
+name: User story
+about: Add a new user story
+title: As `role`, I want `feature`, so I `value`
+labels: ''
+assignees: ''
+
+---
+
+## Acceptance criteria
+
+Write relevant acceptance criteria for this user story in the following format:
+ - [ ] Given `input situation` when `event`, then `outcome`.
+
+## Checklist
+
+Before creating a user story, make sure you have given it the following:
+
+ - [ ] **Milestone:** Sprint [x] (In most cases the current sprint)
+ - [ ] **Importance:** Must / Should / Could / Would
+ - [ ] **Item type:** User Story
+ - [ ] **Priority:** Very High / High / Medium / Low
+
+Make sure you **DON'T** fill in the "Effort" tag, since that is to be decided during a SCRUM poker session.