docs(readme): move contribution guide to a separate file

CONTRIBUTING.md

@@ -0,0 +1,12 @@
+## Contributing 
+
+- With issues:
+  - Use the search tool before opening a new issue.
+  - Please provide source code and commit sha if you found a bug.
+  - Review existing issues and provide feedback or react to them.
+- With pull requests:
+  - Open your pull request against master
+  - Your pull request should have no more than two commits, if not you should squash them.
+  - It should pass all tests in the available continuous integrations systems such as TravisCI.
+  - You should add/modify tests to cover your proposed code changes.
+  - If your pull request contains a new feature, please document it on the README.

README.md

@@ -988,19 +988,6 @@ func main() {
 }
 ```
 
-## Contributing 
-
-- With issues:
-  - Use the search tool before opening a new issue.
-  - Please provide source code and commit sha if you found a bug.
-  - Review existing issues and provide feedback or react to them.
-- With pull requests:
-  - Open your pull request against master
-  - Your pull request should have no more than two commits, if not you should squash them.
-  - It should pass all tests in the available continuous integrations systems such as TravisCI.
-  - You should add/modify tests to cover your proposed code changes.
-  - If your pull request contains a new feature, please document it on the README.
-
 ## Users
 
 Awesome project lists using [Gin](https://github.com/gin-gonic/gin) web framework.