ESQL: Document the existing result-set limitations (elastic#99880)

Document the newly implicit limit of 500 (if no other limit is
provided), as well as the global 10K one.

Related: elastic#99816

docs/reference/esql/index.asciidoc

@@ -92,6 +92,11 @@ POST /_query?format=txt
 ----
 // TEST[setup:library]
 
+The above query's `LIMIT` command limits results to 5 rows.
+
+If not specified, `LIMIT` defaults to `500`. A single query will not return
+more than 10,000 rows, regardless of the `LIMIT` value.
+
 [discrete]
 ==== {kib}
 
@@ -105,20 +110,23 @@ with the time filter.
 [[esql-limitations]]
 === Limitations
 
-{esql} currently supports the following <<mapping-types,field types>>:
-
-- `alias`
-- `boolean`
-- `date`
-- `double` (`float`, `half_float`, `scaled_float` are represented as `double`)
-- `ip`
-- `keyword` family including `keyword`, `constant_keyword`, and `wildcard`
-- `int` (`short` and `byte` are represented as `int`)
-- `long`
-- `null`
-- `text`
-- `unsigned_long`
-- `version`
+* {esql} currently supports the following <<mapping-types,field types>>:
+
+** `alias`
+** `boolean`
+** `date`
+** `double` (`float`, `half_float`, `scaled_float` are represented as `double`)
+** `ip`
+** `keyword` family including `keyword`, `constant_keyword`, and `wildcard`
+** `int` (`short` and `byte` are represented as `int`)
+** `long`
+** `null`
+** `text`
+** `unsigned_long`
+** `version`
+
+* A single query will not return more than 10,000 rows, regardless of the
+`LIMIT` command's value.
 --
 
 include::esql-get-started.asciidoc[]

docs/reference/esql/processing-commands/limit.asciidoc

@@ -7,3 +7,6 @@ The `LIMIT` processing command enables you to limit the number of rows:
 ----
 include::{esql-specs}/docs.csv-spec[tag=limit]
 ----
+
+If not specified, `LIMIT` defaults to `500`. A single query will not return
+more than 10,000 rows, regardless of the `LIMIT` value.