github : update pr template

Author: ggerganov

.github/pull_request_template.md

@@ -1,5 +1,7 @@
-- Self Reported Review Complexity:
-    - [ ] Review Complexity : Low
-    - [ ] Review Complexity : Medium
-    - [ ] Review Complexity : High
-- [ ] I have read the [contributing guidelines](https://github.com/ggerganov/llama.cpp/blob/master/CONTRIBUTING.md)
+
+
+- [x] I have read the [contributing guidelines](https://github.com/ggerganov/llama.cpp/blob/master/CONTRIBUTING.md)
+- Self-reported review complexity:
+  - [ ] Low
+  - [ ] Medium
+  - [ ] High