[DOCS] Added 6.3 info & updated the upgrade table. (elastic#30940)

Author: debadair

docs/reference/upgrade.asciidoc

@@ -40,32 +40,72 @@ required.
 [cols="1<m,1<m,3",options="header",]
 |=======================================================================
 |Upgrade From |Upgrade To |Supported Upgrade Type
-|5.x |5.y |<<rolling-upgrades,Rolling upgrade>> (where `y > x`)
-|5.6 |6.x |<<rolling-upgrades,Rolling upgrade>> footnoteref:[reindexfn, You must delete or reindex any indices created in 2.x before upgrading.]
-|5.0-5.5 |6.x |<<restart-upgrade,Full cluster restart>> footnoteref:[reindexfn]
-|<5.x |6.x |<<reindex-upgrade,Reindex to upgrade>>
-|6.x |6.y |<<rolling-upgrades,Rolling upgrade>> (where `y > x`) 
+|6.0-6.2 |{version} |<<rolling-upgrades,Rolling upgrade>>
+|5.6 |{version} |<<rolling-upgrades,Rolling upgrade>> footnoteref:[reindexfn, You must delete or reindex any indices created in 2.x before upgrading.]
+|5.0-5.5 |{version} |<<restart-upgrade,Full cluster restart>> footnoteref:[reindexfn]
+|Pre-5.0 |{version} |<<reindex-upgrade,Reindex to upgrade>>
 |=======================================================================
 
 [IMPORTANT]
 ===============================================
 
 Elasticsearch can read indices created in the *previous major version*.
-Older indices must be reindexed or deleted. Elasticsearch 6.x
-can use indices created in Elasticsearch 5.x, but not those created in
-Elasticsearch 2.x or before. Elasticsearch 5.x can use indices created in
-Elasticsearch 2.x, but not those created in 1.x or before.
+Older indices must be reindexed or deleted. Elasticsearch 6.n
+can use indices created in Elasticsearch 5.n, but not those created in
+Elasticsearch 2.n or before. Elasticsearch 5.n can use indices created in
+Elasticsearch 2.n, but not those created in 1.n or before.
 
 This also applies to indices backed up with <<modules-snapshots,snapshot
-and restore>>. If an index was originally created in 2.x, it cannot be
-restored to a 6.x cluster even if the snapshot was created by a 5.x cluster.
+and restore>>. If an index was originally created in 2.n, it cannot be
+restored to a 6.n cluster even if the snapshot was created by a 5.n cluster.
 
 Elasticsearch nodes will fail to start if incompatible indices are present.
 
 For information about how to upgrade old indices, see <<reindex-upgrade,
 Reindex to upgrade>>.
 
 ===============================================
+
+[float]
+[[elasticsearch-upgrade-6.3]]
+=== Upgrading to 6.3
+Starting in 6.3, the default distribution includes {xpack} with a free
+Basic license. If you already have a Basic license, once you upgrade to 6.3
+it will never expire or need to be renewed. If you have a license subscription,
+your license and settings are preserved when you upgrade.
+
+You can perform rolling upgrades to 6.3 from OSS-only clusters running 5.6
+or 6.0-6.2. {xpack} Basic features will be operational once the cluster is fully
+upgraded.
+
+If you are using {xpack} for the first time, you must explicitly enable data
+collection after the upgrade to use monitoring. Set
+`xpack.monitoring.collection.enabled` to `true` with the `_cluster/settings`
+API:
+
+[source,json]
+----------------------------------------------------------
+PUT /_cluster/settings
+{
+ "persistent" : {
+ "xpack.monitoring.collection.enabled" : "true"
+ }
+}
+----------------------------------------------------------
+// CONSOLE
+
+To take all of the {xpack} features for a spin, you can start a 30-day trial
+from Kibana, or with the Start Trial API:
+
+[source,json]
+----------------------------------------------------------
+POST _xpack/license/start_trial
+----------------------------------------------------------
+// CONSOLE
+
+The 30-day trial enables you to try out the full set of Platinum features,
+including security, machine learning, alerting, graph capabilities, and more.
+
 --
 
 include::upgrade/rolling_upgrade.asciidoc[]