[zsh] Add some supporting Guix variables

zsh/profile.org

@@ -3,6 +3,25 @@
 Here we set some important variables that are used by other parts of the
 configuration.
 
+** Guix
+
+Set up my Guix profile so that I can use all the right tools.
+
+#+begin_src sh
+  export GUIX_PROFILE="/home/chelys/.guix-profile"
+  source "$GUIX_PROFILE/etc/profile"
+#+end_src
+
+Add the system's data directories to =XDG_DATA_DIRS=. Guix will set the =XDG_DATA_DIRS= environment variable, but this will prevent the rest of the system from using the default ones. This causes a crash in Firefox when I try to upload or download files (well, open a file dialog). According to the [[https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html][XDG Base Directory Specification]]:
+
+#+begin_quote
+If =$XDG_DATA_DIRS= is either not set or empty, a value equal to =/usr/local/share/:/usr/share/= should be used.
+#+end_quote
+
+#+begin_src sh
+  export XDG_DATA_DIRS="${XDG_DATA_DIRS}${XDG_DATA_DIRS:+:}/usr/local/share/:/usr/share/"
+#+end_src
+
 ** XDG
 
   I keep my XDG files in the normal place, but specifying them in an