Add INFOPATH & XDG_DATA_DIRS to nix-profile.sh

This is helpful for locating resources with Nix, especially in
unmanaged situations like on macOS or non-NixOS Linux. Like MANPATH,
it should be harmless to have these set when the directory doesn’t
exist.

scripts/nix-profile.sh.in

@@ -78,6 +78,12 @@ if [ -n "$HOME" ] && [ -n "$USER" ]; then
     if [ -n "${MANPATH}" ]; then
         export MANPATH="$NIX_LINK/share/man:$MANPATH"
     fi
+    if [ -n "${INFOPATH}" ]; then
+        export INFOPATH="$NIX_LINK/share/info:$INFOPATH"
+    fi
+    if [ -n "${XDG_DATA_DIRS}" ]; then
+        export XDG_DATA_DIRS="$NIX_LINK/share:$XDG_DATA_DIRS"
+    fi
 
     export PATH="$NIX_LINK/bin:$__savedpath"
     unset __savedpath NIX_LINK NIX_USER_PROFILE_DIR NIX_PROFILES