ESQL: Updated RENAME docs with the behaviour of multiple column renames

Author: ivancea

docs/reference/query-languages/esql/esql-commands.md

@@ -802,6 +802,8 @@ RENAME old_name1 AS new_name1[, ..., old_nameN AS new_nameN]
 
 The `RENAME` processing command renames one or more columns. If a column with the new name already exists, it will be replaced by the new column.
 
+A `RENAME` with multiple column renames is equivalent to multiple sequential `RENAME` commands.
+
 **Examples**
 
 ```esql
@@ -818,6 +820,15 @@ FROM employees
 | RENAME first_name AS fn, last_name AS ln
 ```
 
+With multiple `RENAME` commands:
+
+```esql
+FROM employees
+| KEEP first_name, last_name
+| RENAME first_name AS fn
+| RENAME last_name AS ln
+```
+
 
 ## `SORT` [esql-sort]