DOC: improved pgpro_build description

Author: Liudmila Mantrova

doc/src/sgml/release-pro-9.6.sgml

@@ -41,7 +41,7 @@
       <listitem>
         <para>
           You can now use <function>pgpro_build</function> function
-          to get the latest commit ID for the current release.
+          to get the latest commit ID for the source files of the current release.
         </para>
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