Added Github packages and gradle to contributing.

Signed-off-by: Dennis Labordus <[email protected]>

Author: Dennis Labordus

.gitignore

@@ -0,0 +1,26 @@
+# SPDX-FileCopyrightText: 2021 Alliander N.V.
+#
+# SPDX-License-Identifier: Apache-2.0
+
+# IDE specific
+.vscode/
+.idea
+
+# General
+.DS_Store
+target
+*.iml
+.settings
+.project
+.classpath
+out
+lib
+bin
+.java-version
+*.orig
+*.rej
+*.swp
+*.swo
+.cache
+build
+

CONTRIBUTING.md

@@ -168,6 +168,40 @@ A Pull Request can't be merged before all SonarCloud issues are being fixed!
 #### Architecture and technologies
 For all architecture and technology choices (for example frameworks, build tools, database choices, etcetera), please check the source code (duh!) and our [CoMPAS Architecture Github Pages](https://com-pas.github.io/compas-architecture/).
 
+#### Github Packages
+To make artifacts between the different GIT repositories available we are using Guthub Packages to ditribute these.
+Every GIT repository can build its artifacts and publish these to Github Packages. 
+Other GIT repositories can then add Github Packages as Maven repository to their build tool.
+See below how to do both action for the specific tools.
+
+To use Github Packages a username and token is needed. The username is your Github username. The token can be genreate in Github by going to your settings, Developer settings, Personal access tokens.
+Generate a new token here and make sure that the scope "read:packages" is enabled. Use this token below to configure the build tools.
+
+#### Basic Gradle
+The project uses Gradle to manage the build. Most projects use multi-module structures to build all code. A basic command to run gradle is:
+```
+$ gradle build
+```
+#### Github Packages in Gradle
+To use Github Packages in Gradle an extra repository need to be added to the build process.
+```
+repositories {
+    ...
+    maven {
+        name = "GitHubPackages"
+        url = uri("https://maven.pkg.github.com/com-pas/*")
+        credentials {
+            username = project.hasProperty('githubUsername') ? project.getProperty("githubUsername") : System.getenv("GITHUB_USERNAME")
+            password = project.hasProperty('githubToken') ? project.getProperty("githubToken") : System.getenv("GITHUB_TOKEN")
+        }
+    }
+    ...
+}
+```
+Because credentials are needed for Github Packages these can be passed in 2 different ways. 
+- First solution is to added the properties "githubUsername" and "githubToken" to your gradle.properties in your home directory (~/.gradle/gradle.properties). This solution doesn't seem to work with Intellij IDEA. 
+- The second solution is to create two environment properties "GITHUB_USERNAME" and "GITHUB_TOKEN". This ones is also used by Github Actions.
+
 #### Basic Maven Usage
 The project uses maven to manage the build. The configuration of all the tools is fairly standard, so if you have already contributed to Java projects, you should feel right at home. You can safely run the full test suite, checkstyle, see code coverage information and the generated documentation with the following command:
 ```