Add only-dirs option to README

README.md

@@ -30,6 +30,7 @@ exa’s options are almost, but not quite, entirely unlike `ls`'s.
 - **-r**, **--reverse**: reverse the sort order
 - **-s**, **--sort=(field)**: which field to sort by
 - **--group-directories-first**: list directories before other files
+- **-D**, **--only-dirs**: list only directories
 - **--git-ignore**: ignore files mentioned in `.gitignore`
 - **-I**, **--ignore-glob=(globs)**: glob patterns (pipe-separated) of files to ignore