typo fix in the documentation (theme_display_rwt => theme_display_rw)

README.md

@@ -58,7 +58,7 @@ set -g theme_display_jobs no
 set -g theme_display_jobs_always yes
 
 ## Hide the current directory read/write indicator.
-set -g theme_display_rwt no
+set -g theme_display_rw no
 
 ## Don't display the VirtualEnv prompt.
 set -g theme_display_virtualent no