Add browser support section to README

+ remove washtml reference

README.md

@@ -26,7 +26,7 @@ The code is mainly written in PHP and is designed to run on a webserver.
 It includes other open-source classes/libraries from [PEAR][pear],
 an IMAP library derived from [IlohaMail][iloha] the [TinyMCE][tinymce] rich
 text editor, [Googiespell][googiespell] (archive) library for spell checking or
-the [WASHTML][washtml] (archive) sanitizer by Frederic Motte.
+the [HTML5-PHP][html5-php] sanitizer by Masterminds.
 
 The current default skin 'Larry' was kindly created by FLINT / Büro für
 Gestaltung, Berne, Switzerland.
@@ -41,6 +41,19 @@ If you're updating an older version of Roundcube please follow the steps
 described in the UPGRADING file.
 
 
+BROWSER SUPPORT
+---------------
+Roundcube uses jQuery 3.x for its client and therefore inherits the browser
+support from there. This currently includes:
+
+- Chrome: (Current - 1) and Current
+- Edge: (Current - 1) and Current
+- Firefox: (Current - 1) and Current, ESR
+- Internet Explorer: 9+
+- Safari: (Current - 1) and Current
+- Opera: Current
+
+
 LICENSE
 -------
 This program is free software: you can redistribute it and/or modify
@@ -93,8 +106,7 @@ hello(at)roundcube(dot)net
 [iloha]:        https://sourceforge.net/projects/ilohamail/
 [tinymce]:      https://www.tiny.cloud/
 [googiespell]:  https://web.archive.org/web/20170314162746/orangoo.com/labs/GoogieSpell/
-[washtml]:      https://web.archive.org/web/20170814135033/http://www.ubixis.com:80/washtml
-[kmgerich]:     http://kmgerich.com/
+[html5-php]:    https://github.com/Masterminds/html5-php
 [gpl]:          https://www.gnu.org/licenses/
 [license]:      https://roundcube.net/license
 [contrib]:      https://roundcube.net/contribute