Update README.md

to add the ranger custom command option

Author: francoiscabrol

README.md

@@ -64,6 +64,14 @@ This can be a problem if you do not have write permissions for the `/tmp` direct
 There is a configuration variable for this called `g:ranger_choice_file`, this must be set to the
 path for a file that doesn't yet exist (this file is created when choosing a file and removed afterwards).
 
+### Setting a custom ranger command
+By default ranger is opened with the command `ranger` but you can set an other custom command by setting the `g:ranger_command_override` variable in your .(n)vimrc.
+
+For instance if you want to display the hidden files by default you can write:
+```
+let g:ranger_command_override = 'ranger --cmd "set show_hidden=true"'
+```
+
 ## Common issues
 
 ### Using fish shell (issue #42)