README.md in prawn-emoji-1.0.1 vs README.md in prawn-emoji-1.0.2

@@ -55,16 +55,24 @@
   * Font size support
 
 ## Supported versions
 
   * Ruby 2.1, 2.2, 2.3
-  * Prawn 1.3, 2.0.2
+  * Prawn 1.3, 2.1
 
 See https://travis-ci.org/hidakatsuya/prawn-emoji.
 
 ## Contributing
 
 Bug reports and pull requests are welcome on GitHub at https://github.com/hidakatsuya/prawn-emoji.
+
+### How to update `emoji/index.yml`
+
+If you update emoji image in `emoji/images`, you need to update `emoji/index.yml` to run the following task:
+
+```
+$ bundle exec rake emoji:generate_index
+```
 
 ## Credit
 
 ### Emoji One