Create CONTRIBUTING.md

Author: farnoodma

CONTRIBUTING.md

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+# How to contribute
+
+First of all, please check out our [general contribution guide](https://github.com/WeAreMahsaAmini/Core/blob/main/CONTRIBUTING.md). Then follow these steps:
+
+1. Join our Discord channel [here](https://discord.gg/ggDH3G8ng2) for related discussions and alignment.
+2. Check out our [Trello board](https://trello.com/b/eeNDR0K2/free-internet) and pick up tasks that are aligned with your skills and start working on them.
+
+> **Note**
+>
+> Tasks on the Trello board may have different labels based on the skills required. Tasks labeled with "Group work" can be picked up by more than one person, and you can usually find them under "In progress" column.
+
+## How to propose new idea and showcase it
+
+If you have new ideas, you can discuss them on our Discord channel or open an issue for it. If enough people gather around your idea, you can start working on it and open PRs for it. Please make sure you use the `new-idea` label on your issue.
+
+If you have implemented something to showcase, please open a PR with the tag `showcase` so we can check it out. Also, it is nice to have a screenshot or video to present the way it works.
+
+## How to make PR
+
+This repo is a public repo under Apache license 2.0. Feel free to open PR based on our templates. Our members will check your changes and if they are ready, we will merge it to the repo.