DOC: documented windows specifics with ICU

Author: Liudmila Mantrova

doc/src/sgml/charset.sgml

@@ -580,6 +580,20 @@ SELECT * FROM test1 ORDER BY a || b COLLATE "fr_FR";
     </para>
    </important>
 
+    <important>
+    <para>
+     On Windows, if the collation provider is <literal>icu</literal>,
+     you cannot use long locale names with the <literal>locale</literal>,
+     <literal>lc_collate</literal>, and <literal>lc_ctype</literal> options.
+     Instead, you must use canonical locale names supported on your
+     operating system. For example, <literal>"ru-RU"</literal> or
+     <literal>"en-US"</literal>. Specifying the encoding with these
+     options is not allowed either. If you need to provide the encoding,
+     use the <literal>--encoding</literal> option. For details on
+     the supported encodings, see <xref linkend="multibyte-charset-supported">.
+    </para>
+   </important>
+
    <para>
      When you start a cluster server or connect to a database,
      <productname>&productname;</> checks that the selected collation