Add info how to authenticate to github packages (#50)

* Add info how to authenticate to github packages

* Remove unneded scopes for PAT

Co-authored-by: Felix Dittrich <31076102+f11h@users.noreply.github.com>

README.md

@@ -32,6 +32,19 @@ The issuer backend is accessed by the [issuer web frontend](https://github.com/e
 - [Open JDK 11](https://openjdk.java.net)
 - [Maven](https://maven.apache.org)
 - [Docker](https://www.docker.com)
+- Authenticate to [Github Packages](https://docs.github.com/en/packages/working-with-a-github-packages-registry/working-with-the-apache-maven-registry)
+
+#### Authenticating in to GitHub Packages
+
+As some of the required libraries (and/or versions are pinned/available only from GitHub Packages) You need to authenticate
+to [GitHub Packages](https://docs.github.com/en/packages/working-with-a-github-packages-registry/working-with-the-apache-maven-registry)
+The following steps need to be followed
+
+- Create [PAT](https://docs.github.com/en/github/authenticating-to-github/creating-a-personal-access-token) with scopes:
+  - `read:packages` for downloading packages
+- Copy/Augment `~/.m2/settings.xml` with the contents of `settings.xml` present in this repository
+  - Replace `${app.packages.username}` with your github username
+  - Replace `${app.packages.password}` with the generated PAT
 
 ### Build