improve markdown

Author: miya0001

README.md

@@ -20,9 +20,7 @@ vendor/bin/phake
 
 *wp-cli.org/package-index is generated by the [package index repo](https://github.com/wp-cli/package-index), and won't be present in your local instance.
 
-### Contribute
-
-## How to translate
+### How to translate
 
 1. Add your language to `[_config.yml](https://github.com/wp-cli/wp-cli.github.com/blob/master/_config.yml)`.
 2. Create a folder under the name of your appropriate language code (IETF language tag). e.g. ja or pt_BR