Add Java and OS recommendations

_opensearch/install/compatibility.md

@@ -0,0 +1,17 @@
+---
+layout: default
+title: Compatibility
+parent: Install OpenSearch
+nav_order: 2
+---
+
+# Operating system and JVM compatibility
+
+- We recommend installing OpenSearch on RHEL- or Debian-based Linux distributions that use [systemd](https://en.wikipedia.org/wiki/Systemd), such as CentOS, Amazon Linux 2, and Ubuntu (LTS). OpenSearch should work on many Linux distributions, but we only test a handful.
+- OpenSearch ships with a compatible version of Java in the `jdk` directory. To find its version, run `./bin/opensearch --version`.
+
+  To use a different Java installation, set the `OPENSEARCH_JAVA_HOME` environment variable to the Java install location. We recommend Java 11 (LTS), but OpenSearch also works with Java 8.
+
+OpenSearch version | Compatible Java versions | Recommended operating systems
+:--- | :--- | :---
+1.x | 8, 11 | Red Hat Enterprise Linux 7, 8; CentOS 7, 8; Amazon Linux 2; Ubuntu 16.04, 18.04, 20.04

_opensearch/install/docker.md

@@ -2,7 +2,7 @@
 layout: default
 title: Docker
 parent: Install OpenSearch
-nav_order: 1
+nav_order: 3
 ---
 
 # Docker image
@@ -16,7 +16,7 @@ docker pull opensearchproject/opensearch-dashboards:{{site.opensearch_version}}
 
 To check available versions, see [Docker Hub](https://hub.docker.com/u/opensearchproject).
 
-OpenSearch images use `centos:7` as the base image. If you run Docker locally, we recommend allowing Docker to use at least 4 GB of RAM in **Preferences** > **Resources**.
+OpenSearch images use `amazonlinux:2` as the base image. If you run Docker locally, set Docker to use at least 4 GB of RAM in **Preferences** > **Resources**.
 
 
 ---