RELEASE.txt: notes that print.php is implemented.

extension/RELEASE.txt

@@ -12,6 +12,15 @@ Changes
        'pattern','allbut','all') NOT NULL DEFAULT 'alnumx'
 
 
+Features
+--------
+
+ * print.php
+
+   * Install `wkhtmltopdf` on the webserver (http://wkhtmltopdf.org/).
+   * In config.qfq.ini setup BASE_URL_PRINT, WKHTMLTOPDF.
+
+
 Bug Fixes
 ---------