add a pull request template (superdesk#154)

* add a pull request template

* add a line on lodash.get

.github/pull_request_template.md

@@ -0,0 +1,8 @@
+## Front-end checklist
+
+<!--- Go over all the following points, and put an `x` in all the boxes that apply. -->
+- [ ] This pull request is replacing `lodash.get` with optional chaining and nullish coalescing for modified code segments
+- [ ] This pull request is adding missing TypeScript types to modified code segments where it's easy to do so with confidence
+- [ ] This pull request is using `memo` or `PureComponent` to define new React components (and updates existing usages in modified code segments)
+- [ ] This pull request is not importing anything from client-core directly (use `superdeskApi`)
+- [ ] This pull request is importing UI components from `superdesk-ui-framework` and `superdeskApi` when possible instead of using ones defined in this repository.