Slight readme improvements

Author: benlk

README.md

@@ -37,10 +37,12 @@ For example, the shortcode `[pym src="http://blog.apps.npr.org/pym.js/examples/g
 <div id="extremely_specific_example" class="pym"></div><script src="http://example.org/wp-content/plugins/pym-shortcode/js/pym.v1.min.js"></script><script>var pym_0 = new pym.Parent('extremely_specific_example', 'http://blog.apps.npr.org/pym.js/examples/graphic/child.html', {})</script>
 ```
 
-`class` is optional; this should be a valid HTML class name. It will be added to the element's default class, `'pym'`. You would want to use this is, for example, you wanted to [use a size-based class name to determine the size of the embed on your site](https://github.com/INN/pym-shortcode/issues/23). The class `'pym'` will always be output on container elements created by the Pym Shortcode. This class was introduced in version 1.2.2.
+`class` is optional; this should be a valid HTML class name. It will be added to the element's default class, `'pym'`. You would want to use this if, for example, you wanted to [use a size-based class name to determine the size of the embed on your site](https://github.com/INN/pym-shortcode/issues/23). The class `'pym'` will always be output on container elements created by the Pym Shortcode. This class was introduced in version 1.2.2.
 
 For example, the shortcode `[pym src="http://blog.apps.npr.org/pym.js/examples/graphic/child.html" class="one two three four float-left mw_50"]` results in the following output:
 
 ```html
 <div id="pym_0" class="pym one two three four float-left mw_50"></div><script src="http://insideenergy.dev/wp-content/plugins/pym-shortcode/js/pym.v1.min.js"></script><script>var pym_0 = new pym.Parent('pym_0', 'http://blog.apps.npr.org/pym.js/examples/graphic/child.html', {})</script>
 ```
+
+If you do not want the class `'pym'` output on container elements, [add a filter](https://codex.wordpress.org/Plugin_API/Filter_Reference) to the hook `pym_shortcode_default_class` that returns an empty string.

readme.txt

@@ -50,7 +50,7 @@ Mobile view of the WordPress post with the NPR embed using Pym Shortcode:
 * (we skipped pym.js version 1.2.1: https://github.com/nprapps/pym.js/releases/tag/v1.2.1 )
 * Add `id=""` attribute to allow setting custom IDs on embeds. [#21](https://github.com/INN/pym-shortcode/issues/21)
 * Add `class=""` attribute to allow setting custom classes on embeds. [#22](https://github.com/INN/pym-shortcode/issues/22) and [#23](https://github.com/INN/pym-shortcode/issues/23).
-* Add a default class name `pym` to all embeds output by this plugin.
+* Add a default class name `pym` to all embed-containing div elements output by this plugin, and a filter 'pym_shortcode_default_class' to allow changing it.
 
 = 1.2.0.2 =