[DOCS] Added forecast limitations (elastic/x-pack-elasticsearch#3503)
[DOCS] Added forecast limitations (elastic/x-pack-elasticsearch#3503)

Original commit: elastic/x-pack-elasticsearch@24149658bc6f5d60cd0708f48e42682b7c1e46c5

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