📝 Add README and some concepts

README.md

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+# Matrix.Nucleus
+
+The server-side software for Matrix.Marketplace.
+Which is a software distribution marketplace that made from developer & for developer.
+
+> ![NOTE]
+> Matrix is now a part of the HyperNet project. To run it yourself, you should run the service gateway Nexus and its dependencies.
+> Learn more from Nexus project here: <https://github.com/Solsynth/HyperNet.Nexus>
+
+## Concepts
+
+One of the core concepts of Matrix is the **Product**.
+We call a single application, or a game or something else a product.
+
+When you want to release something like executable or something else.
+You will need to create a **Release**.
+
+The release is belongs to a product, which a product has multiple releases.
+
+The release has a **Version**. Which follow the [Semantic Versioning](https://semver.org)
+for better understanding and version comparison.
+
+The release has also a channel, which different channel subscribers will receive different releases.
+Like the beta, canary and the stable channel. You can add anything you want.
+
+For user to download the release, there has an **Assets** field on the release.
+The assets is a Dictionary of the files to download for different platform, the key is the platform id.
+And the value is list of the compressed assets files or links.
+
+> The file serving is powered by our [Paperclip](https://github.com/Solsynth/HyperNet.Paperclip) project. We're really proud of it.
+
+### Updates
+
+About the release, we got two types of the release, full release and increment one.
+
+For new users, it will need to download the latest full release and all the increment releases after it,
+and our app will merge all the release into a working one.
+
+For the old users that already have the previous release, it will download the latest increment one
+and apply it to the local one.