Added entry for mur.at https://mur.at

Hi folks! We at mur.at deployed our librehost.json to out webpage https://mur.at
and kindly ask for merging the updated directory.json into master :-) cheers from NOC@mur.at in Graz, Austria ralph

directory.json

@@ -12,6 +12,7 @@
 "Infini" : "https://www.infini.fr/librehost.json",
 "LibreOps" : "https://libreops.cc/librehost.json",
 "LinuxPizza" : "https://linux.pizza/librehost.json",
+"mur.at" : "https://mur.at/librehost.json",
 "Nomagic" : "https://nomagic.uk/librehost.json",
 "Petites Singularités" : "https://ps.lesoiseaux.io/librehost.json",
 "snopyta.org" : "https://snopyta.org/librehost.json",