Update PULL_REQUEST_TEMPLATE.md

Author: nmetulev

.github/PULL_REQUEST_TEMPLATE.md

@@ -19,7 +19,7 @@ Closes # <!-- REQUIRED: Add the issue number (ex: #12) so the issue is automatic
 ### PR checklist
 - [ ] Project builds (`npm run build`) and changes have been tested in supported browsers (including IE11)
 - [ ] All public classes and methods have been documented
-- [ ] Added appropriate [documentation](https://github.com/microsoftgraph/microsoft-graph-docs/tree/master/concepts/toolkit)
+- [ ] Added appropriate [documentation](https://github.com/microsoftgraph/microsoft-graph-docs/tree/master/concepts/toolkit) [target branch `mgt/next` for new features]. Docs PR: <!-- Link to docs PR here -->
 - [ ] License header has been added to all new source files (`npm run setLicense`)
 - [ ] Contains **NO** breaking changes