ESQL small doc improvement (#101226)

Move command list to the top

Co-authored-by: Alexandros Batsakis <abatsakis@splunk.com>

docs/reference/esql/esql-commands.asciidoc

@@ -8,7 +8,7 @@
 // tag::source_commands[]
 ==== Source commands
 
-An {esql} source command produces a table, typically with data from {es}.
+An {esql} source command produces a table, typically with data from {es}. An {esql} query must start with a source command.
 
 image::images/esql/source-command.svg[A source command producing a table from {es},align="center"]
 
@@ -18,10 +18,6 @@ image::images/esql/source-command.svg[A source command producing a table from {e
 * <<esql-row>>
 * <<esql-show>>
 
-include::source-commands/from.asciidoc[]
-include::source-commands/row.asciidoc[]
-include::source-commands/show.asciidoc[]
-
 // end::source_command[]
 
 // tag::proc_commands[]
@@ -47,6 +43,12 @@ image::images/esql/processing-command.svg[A processing command changing an input
 * <<esql-stats-by>>
 * <<esql-where>>
 
+// end::proc_command[]
+
+include::source-commands/from.asciidoc[]
+include::source-commands/row.asciidoc[]
+include::source-commands/show.asciidoc[]
+
 include::processing-commands/dissect.asciidoc[]
 include::processing-commands/drop.asciidoc[]
 include::processing-commands/enrich.asciidoc[]
@@ -59,5 +61,3 @@ include::processing-commands/rename.asciidoc[]
 include::processing-commands/sort.asciidoc[]
 include::processing-commands/stats.asciidoc[]
 include::processing-commands/where.asciidoc[]
-
-// end::proc_command[]