Create CONTRIBUTING.md

First guideline for contribution.

CONTRIBUTING.md

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+This page guides a format for your contribution.
+
+## Commit Message
+[Module][Feature] - [Title]
+
+[Description]
+##
+
+- [Module] is a sub module majorly affected by your change. Most of times this indicates a sub folder name.
+This indicates whom need to review your patch as well.
+If your change don't belonged to any sub modules, you can replace with proper name or skip it.
+The name must be written in all lower alphabet characters.
+  - ex) build / doc / infra / common / sw_engine / gl_engine / svg_loader / examples / wasm / svg2png  ...
+
+- [Feature] is what major function/feature you changed. Normally this indicates a representive file name. 
+You can keep the file name, but don't please contain any prefix(tvg) nor suffix(Impl) here.
+  - ex) Canvas / TaskScehduler / SvgLoader / SvgBuilder / SwRle / GlRenderer / ...
+
+- [Title] is a brief description of your change. It must be described in one sentence.
+  - ex) "Fixed a typo"
+  - ex) "Fixed compile warnings"
+  - ex) "Code refactoring"
+  - ex) "Fixed a rendering bug that overlapped shapes inproper way."
+  
+- [Description] There is no any strict formats, but it must describe what you did in this patch as far as possible you can describe in detail.
+
+  If you fixed any bugs, it must contain below:
+  - what type of bug  
+  - conditions to reproduce it
+  - root cause
+  - solution 
+  
+  Or if you add a new feature or function, it must contain below:
+  - what sort of features
+  - api full specification (if any api additions)
+  - any necessity
+  - condition / restriction  
+  - reference or sample
+  
+  Lastly, please append any issue ticket numbers in this section if any.
+  
+  - ex) common composite: newly added path clipping feature
+
+    We introduced new method Paint::composite() to support composite behaviors. </br>
+    This allows paints to composite with other paints instances. </br>
+    Composite behaviors depends on its compoite method type. </br>
+    Here we firstly introduced "ClipPath" method to support clipping by path unit of paint.</br>    
+    
+    tagetPaint->composite(srcPaint, CompoisiteMethod::ClipPath);</br>
+    
+    Beaware if the source paint doesn't contain any path info, clipping won't be applied as you expected.
+    
+    @API Additions:</br>
+    enum CompositeMethod {None = 0, ClipPath}; </br>
+    Result Paint::composite(std::unique_ptr<Paint> target, CompMethod method) const noexcept;</br>
+
+    @Examples: added ClipPath</br>
+
+    @Issues: 49
+  
+