Add PR template (#227)

This PR template is for team members to fill required details on PR to
ease the process of PR review & provide a checklist for important items
not to be forgotten.

.github/pull_request_template.md

@@ -0,0 +1,21 @@
+### Description
+<!-- Describe what change this PR is implementing -->
+
+### Types of Changes
+<!--- What types of changes does your code introduce? -->
+- [ ] Bug fix (non-breaking change which fixes an issue)
+- [ ] New feature (non-breaking change which adds functionality)
+- [ ] Breaking change (fix or feature that would cause existing functionality to change)
+- [ ] Dependency upgrade (A change in substrate or any 3rd party crate version)
+
+### Migrations and Hooks
+<!--- Check the following box with an x if the following applies: -->
+- [ ] This change requires a runtime migration.
+- [ ] Modifies `on_initialize`
+- [ ] Modifies `on_finalize`
+
+### Checklist
+<!--- All boxes need to be checked. Follow this checklist before requiring PR review -->
+- [ ] Change has been tested locally.
+- [ ] Change adds / updates tests.
+- [ ] Changelog doc updated.