Doc: Replace mention to "K bytes" by "kilobytes" in textsearch.sgml

"kB" or "kilobyte" is used in the documentation.

Author: Daniel Gustafsson
Discussion: https://postgr.es/m/32BA3AF7-37E9-4334-A226-98B844ADCC4E@yesql.se

Author: michaelpq

doc/src/sgml/textsearch.sgml

@@ -3915,7 +3915,7 @@ Parser: "pg_catalog.default"
    text search features are:
    <itemizedlist  spacing="compact" mark="bullet">
     <listitem>
-     <para>The length of each lexeme must be less than 2K bytes</para>
+     <para>The length of each lexeme must be less than 2 kilobytes</para>
     </listitem>
     <listitem>
      <para>The length of a <type>tsvector</type> (lexemes + positions) must be