Add note on mapping limitation

Author: bobbyatsegment

src/connections/destinations/catalog/eloqua/index.md

@@ -123,6 +123,9 @@ formatting-insensitive match so that if you have a field called `Account Type`
 in Eloqua and a property called `AccountType` in your Segment event, the
 mapping will get handled.
 
+> info "Track event mapping limitations"
+> Each track event can only be mapped to a single custom object; mapping a single track event to multiple custom objects is not supported.
+
 For `track` event properties you intend to send to Eloqua as Custom Object
 fields, make sure the value of the data type sent to Segment matches the
 data type specified in your Eloqua dashboard. If a Custom Object field data