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CONTRIBUTING.md

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+# Contributing Guidelines
+Thank you for your contributing! My requirements are few things. Please read them.
+
+## Issue
+Thank you for feedback. When you report a problem, please pay attention to fowllowing points.
+
+### Does it happen on web browsers? (especially Chrome)
+electron-mattermost is based on Electron. It integrates Chrome as a browser window. If the problem appears on web browsers, it may be the issue for Mattermost (or Chrome).
+
+### Write detailed information
+Following points are important to understand the problem.
+
+* electron-mattermost version
+* OS
+* Mattermost version
+* Expected behavior (or what is wrong)
+* How to reproduce, step-by-step
+
+## Pull request
+PR is welcome.
+
+When you edit the code, please run `npm run prettify` before your `git commit`.
+Codes will be formatted.
+
+Then, such as following points are helpful.
+
+* Tested OS
+* Tested Mattermost version
+* Test codes for your changes