Document ARRAY_SLICE in pg mode

h2/src/docsrc/html/features.html

@@ -959,6 +959,7 @@ or the SQL statement <code>SET MODE PostgreSQL</code>.
 </li><li>Fixed-width strings are padded with spaces.
 </li><li>MONEY data type is treated like NUMERIC(19, 2) data type.
 </li><li>Datetime value functions return the same value within a transaction.
+</li><li>ARRAY_SLICE() out of bounds parameters are silently corrected.
 </li></ul>
 
 <h3>Ignite Compatibility Mode</h3>