docs(environmental variables): Make referable

Author: tony

docs/configuration/environmental-variables.md

@@ -2,10 +2,14 @@
 
 # Environmental variables
 
+(TMUXP_CONFIGDIR)=
+
 ## `TMUXP_CONFIGDIR`
 
 Example: `TMUXP_CONFIGDIR=$HOME/.mytmuxpconfigdir tmuxp load cpython`
 
+(LIBTMUX_TMUX_FORMAT_SEPARATOR)=
+
 ## `LIBTMUX_TMUX_FORMAT_SEPARATOR`
 
 :::{seealso}