The documentation has been added.
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+# UltimateKEYS - Xmodmap (Linux)
+
+Xmodmap deployment on GNU/Linux :
+
+- Put the file ".Xmodmap" into the user's home directory (~).
+- On, for instance, EndeavourOS XFCE and Kubuntu, "~/.Xmodmap" should automatically load when logging in, on some other distributions, it can be activated via :
+xmodmap ~/.Xmodmap - or - xmodmap $HOME/.Xmodmap
+- *Unfortunately, it turns out that Xmodmap is no longer supported on Gnome.*