Merge pull request #655 from mendix/readme_update_4x

readme update: jvm garbage collector var and warning for mx10

README.md

@@ -7,6 +7,8 @@ This document contains general information on the Mendix Cloud Foundry Buildpack
 The buildpack is heavily tied to the Mendix Public Cloud, but can be used independently.
 Release notes are available for the [buildpack](https://github.com/mendix/cf-mendix-buildpack/releases/), [Mendix itself](https://docs.mendix.com/releasenotes/studio-pro/) and the [Mendix Public Cloud](https://docs.mendix.com/releasenotes/developer-portal/deployment).
 
+**⚠️ Warning** At this time, CF Buildpack doesn't support building Mendix 10 MPK files. To deploy a Mendix 10 app with CF Buildpack, you will need to build the MDA file first (using Studio Pro 10 or [MxBuild](https://docs.mendix.com/refguide/mxbuild/)), and deploy the MDA file using CF Buildpack.
+
 * [Requirements](#requirements)
 * [Supported Mendix Versions](#supported-mendix-versions)
 * [Buildpack Releases and Version Pinning](#buildpack-releases-and-version-pinning)
@@ -449,6 +451,14 @@ The Java Max Metaspace Size is configured automatically based on best practices.
 cf set-env <YOUR_APP> MAX_METASPACE_SIZE 512M
 ```
 
+### Java Garbage Collector
+
+The Java garbage collector is configured automatically based on best practices. You can tweak this to your needs by using another environment variable, the accepted values are Serial or G1.
+
+```shell
+cf set-env <YOUR_APP> JVM_GARBAGE_COLLECTOR Serial
+```
+
 ### Java Virtual Machine (JVM) Settings
 
 You can configure the Java properties by providing the `JAVA_OPTS` enviroment variable to the application.