Add doc to README

README.md

@@ -7,3 +7,40 @@ puppet-lint-empty_string-check
 [![Coverage Status](https://img.shields.io/coveralls/camptocamp/puppet-lint-empty_string-check.svg)](https://coveralls.io/r/camptocamp/puppet-lint-empty_string-check?branch=master)
 
 A puppet-lint plugin to check for variables assigned to the empty string.
+
+
+## Checks
+
+### Variable assigned to the empty string
+
+The empty string is true in the future parser. `undef` should be used instead for a false value for strings.
+
+
+#### What you have done
+
+```puppet
+$foo = ''
+```
+
+#### What you should have done
+
+```puppet
+$foo = undef
+```
+
+Note: There are valid cases of assigning a variable to the empty string. You should use [control comment](http://puppet-lint.com/controlcomments/) to disable checks for these.
+
+
+#### Disabling the check
+
+To disable this check, you can add `--no-empty_string_assignment-check` to your puppet-lint command line.
+
+```shell
+$ puppet-lint --no-empty_string_assignment-check path/to/file.pp
+```
+
+Alternatively, if you’re calling puppet-lint via the Rake task, you should insert the following line to your `Rakefile`.
+
+```ruby
+PuppetLint.configuration.send('disable_empty_string_assignment')
+```