[DOCS] Update X-Pack installation instructions (elastic/x-pack-elasticsearch#4110)
[DOCS] Update X-Pack installation instructions (elastic/x-pack-elasticsearch#4110)

Original commit: elastic/x-pack-elasticsearch@e7f97d5a3a442791d2572db1eb5aa7da238bee29

strapdata/elassandra,strapdata/elassandra,vroyer/elassandra,strapdata/elassandra,strapdata/elassandra,vroyer/elassandra,vroyer/elassandra,strapdata/elassandra