Update UPGRADE for 2.1 release

UPGRADE.md

@@ -1,6 +1,29 @@
 # Upgrade
 
-## dev-release/2.0
+## 2.1.0
+
+### Elasticsearch Upgrade
+
+We now use an own fork of the elasticsearch packages to provide Elasticsearch 7 support.
+For upgrading you can use the following commands:
+
+```bash
+# Remove ongr packages:
+composer remove ongr/elasticsearch-bundle --no-update
+composer remove ongr/elasticsearch-dsl --no-update
+
+# Use your matching elasticsearch version here ( ^5, ^6 or ^7 ):
+composer require elasticsearch/elasticsearch:"^7" --no-update
+
+# Update article bundle to newest version:
+composer require sulu/article-bundle:"^1.2" --with-dependencies
+
+# Reindex your articles when upgrading elasticsearch version:
+bin/adminconsole ongr:es:index:create --manager default
+bin/adminconsole ongr:es:index:create --manager live
+bin/adminconsole sulu:article:reindex
+bin/websiteconsole sulu:article:reindex
+```
 
 ### Mapping of index changed