Readme upgrade notice too long

Hi there,

As shown in the example readme, the upgrade notice shouldn’t be longer than 300 characters.

It’s currently cut off, and because of core CSS it flows over the screen.
This means the following is output:

2.6 is a major update so it is important that you make backups, and ensure themes and extensions are 2.6 compatible before upgrading. Developers should catch up with the development blog to see what has been happening in core. Note: 2.6 includes Shipping Zone functionality. Please ensure shipping m

Which will/might leave people to confusion :).

Enjoy your day!

https://wordpress.org/plugins/woocommerce/