Add new Contributing Code file

Documentation/source/Readme/Contributing Code

+Contributing Code
+#################
+
+Start Contributions
+*******************
+Code Style
+==========
+
+Develop, review, and test code following the OpenHarmony coding standards. Make sure code is written in the same style.
+
+* C++ Coding Style Guide
+* C Coding Style Guide
+* JavaScript Coding Style Guide
+* Python Coding Style Guide
+
+Contribution Workflow
+*********************
+
+For details, see Contribution Process.
+
+Security Issue Disclosure
+*************************
+* Security handling procedure
+* Security disclosure information
\ No newline at end of file