Create CONTRIBUTING.md

Author: AB-xdev

CONTRIBUTING.md

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+## Contributing
+
+We would absolutely love to get the community involved, and we welcome any form of contributions – comments and questions on different communication channels, issues and pull request and anything that you build and share using our components.
+
+### Communication channels
+* Communication is primarily done using issues.
+* If you need support as soon as possible and you can't wait for any pull request, feel free to use [our support](https://xdev.software/en/services/support).
+* As a last resort measure or on otherwise important matter you may also [contact us directly](https://xdev.software/en/about-us/contact).
+
+### Ways to help
+* **Report bugs**<br/>Create an issue or send a pull request
+* **Send pull requests**<br/>If you want to contribute code, check out the development instructions below.
+  * However when contributing new features, please first discuss the change you wish to make via issue with the owners of this repository before making a change. Otherwise your work might be rejected and your effort was pointless.
+
+We also encourage you to read the [contribution instructions by GitHub](https://docs.github.com/en/get-started/quickstart/contributing-to-projects).
+
+## Developing
+
+### Software Requirements
+You should have the following things installed:
+* Git
+* Java 17 - should be as unmodified as possible (Recommended: [Eclipse Adoptium](https://adoptium.net/temurin/releases/))
+* Gradle (shipped inside the repo as Gradle Wrapper - also available inside IntelliJ)
+
+### Recommended setup
+* Install ``IntelliJ`` (Community Edition is sufficient)
+  * Install the following plugins:
+    * [Save Actions](https://plugins.jetbrains.com/plugin/22113) - Provides save actions, like running the formatter or adding ``final`` to fields
+    * [SonarLint](https://plugins.jetbrains.com/plugin/7973-sonarlint) - CodeStyle/CodeAnalysis
+    * [Checkstyle-IDEA](https://plugins.jetbrains.com/plugin/1065-checkstyle-idea) - CodeStyle/CodeAnalysis
+    * [Plugin DevKit](https://plugins.jetbrains.com/plugin/22851) - IntelliJ Plugin development
+  * Import the project
+  * Ensure that everything is encoded in ``UTF-8``
+  * Ensure that the JDK/Java-Version is correct
+
+## Development environment
+
+<i>See also [JetBrains Docs for developing IntelliJ Plugins](https://plugins.jetbrains.com/docs/intellij/developing-plugins.html)</i>
+
+The plugin is built with gradle, but you don't need to install it if you build with the Intellij gradle plugin (check out the [prerequisites](https://plugins.jetbrains.com/docs/intellij/plugin-required-experience.html)). If you don't intend to use the Intellij gradle plugin, you can use native gradle (replace `./gradlew` by `gradle`).
+
+Start idea and import the `build.gradle` file with "File > Open". Then in the "Import Project from Gradle" window, make sure you check "Use gradle 'wrapper' task configuration" before clicking "Finish". You now have a gradle wrapper installed (`gradlew`) that you can use on the command line to generate idea folders:
+
+```bash
+# Initialize idea folders
+./gradlew cleanIdea idea
+```
+
+IntelliJ should refresh and the project is now configured as a gradle project. You can find IntelliJ gradle tasks in "Gradle > Gradle projects > intellij-plugin-template > Tasks > intellij". To run the plugin, use the `runIde` task:
+
+```bash
+# Run the plugin (starts new idea)
+./gradlew runIde
+```
+
+## Releasing [![Build](https://img.shields.io/github/actions/workflow/status/xdev-software/intellij-plugin-template/release.yml?branch=master)](https://github.com/xdev-software/intellij-plugin-template/actions/workflows/release.yml)
+
+Before releasing:
+* Consider doing a [test-deployment](https://github.com/xdev-software/intellij-plugin-template/actions/workflows/test-deploy.yml?query=branch%3Adevelop) before actually releasing.
+* Check the [changelog](CHANGELOG.md)
+
+If the ``develop`` is ready for release, create a pull request to the ``master``-Branch and merge the changes
+
+When the release is finished do the following:
+* Merge the auto-generated PR (with the incremented version number) back into the ``develop``
+