README: add buttons to irc and matrix
README: add buttons to irc and matrix

RSS-Bridge/rss-bridge,kranack/rss-bridge,Riduidel/rss-bridge,Riduidel/rss-bridge,Riduidel/rss-bridge,ORelio/rss-bridge,kranack/rss-bridge,ORelio/rss-bridge,RSS-Bridge/rss-bridge,RSS-Bridge/rss-bridge,kranack/rss-bridge,kranack/rss-bridge,ORelio/rss-bridge