doc: keyboard layout documentation

nix/nixosModules/extra/layouts/README.md

@@ -4,6 +4,7 @@ This folder contains my very awesome dvorak French layout on linux
 `$XDG_CONFIG_HOME/.config/xkb` doesn't work.
 [source](https://github.com/elias19r/xkb-layouts)
 
+NOTE: make sure the copied file has no extension, otherwise your x11 will crash.
 `# cp dvorak-french.xkb /usr/share/X11/xkb/symbols/`
 
 `/usr/share/X11/xkb/rules/evdev.xml`
@@ -33,6 +34,7 @@ This folder contains my very awesome dvorak French layout on linux
 
 # Notes
 Use `setxkbmap -option caps:swapescape` to swap escape and capslock
+It is possible to reset this option by using the `-option` flag without any argument.
 [source](https://askubuntu.com/a/830343)
 
 ## Sources