Minor documentation fix - missing blank space

Hi,

When I read the documentation about Overview of PostgreSQL Internals - Executor [1]https://www.postgresql.org/docs/14/executor.html,
I find there is a missing space in the documentation.

diff --git a/doc/src/sgml/arch-dev.sgml b/doc/src/sgml/arch-dev.sgml
index 7aff059e82..c2be28fac8 100644
--- a/doc/src/sgml/arch-dev.sgml
+++ b/doc/src/sgml/arch-dev.sgml
@@ -559,7 +559,7 @@
     A simple <command>INSERT ... VALUES</command> command creates a
     trivial plan tree consisting of a single <literal>Result</literal>
     node, which computes just one result row, feeding that up
-    to<literal>ModifyTable</literal> to perform the insertion.
+    to <literal>ModifyTable</literal> to perform the insertion.
    </para>

</sect1>

[1]: https://www.postgresql.org/docs/14/executor.html

--
Regrads,
Japin Li.
ChengDu WenWu Information Technology Co.,Ltd.