Update README

README.md

@@ -183,8 +183,8 @@ fkill() {
 }
 ```
 
-Key bindings
-------------
+Key bindings for command line
+-----------------------------
 
 The install script will add the following key bindings to your configuration
 files.
@@ -360,6 +360,20 @@ when it's running on Ruby 1.8. If you experience the problem, upgrade your Ruby
 to 1.9 or above. Ruby 1.9 or above is also required for displaying Unicode
 characters.
 
+### Ranking algorithm
+
+fzf sorts the result first by the length of the matched substring, then by the
+length of the whole string. However it only does so when the number of matches
+is less than the limit which is by default 1000, in order to avoid the cost of
+sorting a large list and limit the response time of the query.
+
+This limit can be adjusted with `-s` option, or with the environment variable
+`FZF_DEFAULT_SORT`.
+
+```sh
+export FZF_DEFAULT_SORT=10000
+```
+
 License
 -------