Add template for PR targeted to develop branch

All PR description should be unified by some template. This commit provides such template file

Author: AKalinich-Luxoft

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,12 @@
+Implements/Fixes [#nnnn](github.com/smartdevicelink/sdl_core/issues/nnnn)
+
+This PR is **[ready / not ready]** for review.
+
+### Testing Plan
+[Describe how your changes will be tested]
+
+### Summary
+[Summary of PR changes]
+
+### CLA
+- [ ] I have signed [the CLA](https://docs.google.com/forms/d/e/1FAIpQLSdsgJY33VByaX482zHzi-xUm49JNnmuJOyAM6uegPQ2LXYVfA/viewform)