Updated Installation (markdown)

Installation.md

@@ -554,10 +554,36 @@ Click on `Edit` button on the right, scroll down to *Supplementary files* box
 and upload the compiled `javarun.class`.
 
 
+#### Java Maven (for larger projects)
+
+This environment requires OpenJDK to be installed (see Java environment), but
+you do not have to have Java environment itself enabled in ReCodEx.
+
+Install Apache Maven manually by extracting `tar.gz` binaries into `/opt/maven`.
+Most manuals will have you install Maven into something like `/opt/apache-maven-3.8.4`,
+but the version in the path would make it difficult for upgrades (and the pipelines
+are already configured for `/opt/maven`).
+
+Maven requires cache for dependencies pre-built, since the sandbox is not allowed
+to modify it and it would be tedious to reload everything with every project.
+Checkout/download [utility for building `.m2` cache](https://github.com/ReCodEx/utils/tree/master/maven-m2-builder).
+There is a reference project (hello world), which is built and executed by the
+`build.sh` script. It populates `.m2` directory and then moves it to `/opt/maven-repo`
+(`sudo` is used for moving, so the current user must be a sudoer). The `pom.xml` of the reference
+project contains some dependencies we find useful, feel free to add your own
+(note that you need to edit the `pom.xml.template`).
+
+Finally, add the following variables to `environ-variable` list in the worker configuration:
+```
+MAVEN_HOME: /opt/maven
+M2_HOME: /opt/maven-repo
+```
+
+
 #### Kotlin
 
-This environment requires Java runtime to be installed as well (please do before
-venturing forth).
+This environment requires OpenJDK to be installed (see Java environment), but
+you do not have to have Java environment itself enabled in ReCodEx.
 
 Download latest Kotlin compiler release from [GitHub](https://github.com/JetBrains/kotlin)
 and unzip it to `/opt/kotlin`.