OpenSSF: add 'Contribution' and 'Report a problem' to README.md (#536)

Address #516

Author: wenju-he

README.md

@@ -132,3 +132,11 @@ following files:
 `-- lib64
     `-- libLLVMSPIRVLib.so
 ```
+
+## Contribution
+Please submit a pull request to contribute.
+
+Please follow [LLVM coding standards](https://llvm.org/docs/CodingStandards.html)
+
+## Report a problem
+Please submit an [issue](https://github.com/intel/opencl-clang/issues)