SiliconLabsGH-14: Enable CLA contribs

Bug-SiliconLabs: UIC-3082
Bug-GitHub: rzr#3
Relate-to: SiliconLabs#14
Forwarded: https://github.com/SiliconLabs/UnifySDK/pulls/rzr
Signed-off-by: Philippe Coval <philippe.coval@silabs.com>

Author: rzr

.github/pull_request_template.md

@@ -0,0 +1,16 @@
+## Change
+<!--
+  Describe your changes below.
+  Feel free to add context (internal references are encouranged in commit messages as well, align to others)
+-->
+
+## Checklist
+<!--
+  Please put an `x` in each box to make sure to enable contribution process
+-->
+
+- [ ] A [Contribution License Agreement][CLA] has been established between @SiliconLabs and author's company (matching email domain)
+
+[CLA]: https://en.wikipedia.org/wiki/Contributor_License_Agreement
+
+