Create pull request template (#821)

## Pull request template

This PR creates a pull request template that will be used for all pull
requests, to make them consistent and always provide enough information
about what was changes / what was added

**The PR template looks like this:**

## Issues connected

Resolves

## What has been done

- Change 1

## Testing

- [ ] Test 1

## Screenshots / images / videos

Please provide assets necessary for the PR (remove if not applicable)

**Open to suggestions, what should be changed / what should be added**

.github/pull_request_template.md

@@ -0,0 +1,15 @@
+## Issues connected
+
+Resolves
+
+## What has been done
+
+- Change 1
+
+## Testing
+
+- [ ] Test 1
+
+## Screenshots / images / videos
+
+Please provide assets necessary for the PR (remove if not applicable)