Mention that toplevel is part of pg_stat_statements key.
While at it, also document that toplevel is always true if
pg_stat_statements.track is set to top.
Author: Julien Rouhaud
Reported-By: Fujii Masao
Discussion:
<para>
The statistics gathered by the module are made available via a
view named <structname>pg_stat_statements</structname>. This view
- contains one row for each distinct database ID, user ID and query
- ID (up to the maximum number of distinct statements that the module
+ contains one row for each distinct database ID, user ID, query ID and
+ toplevel (up to the maximum number of distinct statements that the module
can track). The columns of the view are shown in
<xref linkend="pgstatstatements-columns"/>.
</para>
</para>
<para>
True if the query was executed as a top level statement
+ (if <varname>pg_stat_statements.track</varname> is set to
+ <literal>all</literal>, otherwise always false)
</para></entry>
</row>
