Rewrite description for URL alias on node/add/*

Problem/Motivation

The description for the URL alias on node add forms is confusing.

Proposed resolution

Change the description.

Remaining tasks

A patch needs to be created that changes the description.

User interface changes

The description of the the url alias field gets changed.

API changes

None.

Data model changes

None.

Original report by @ET205

Note: This issue is being posted here as an exercise by a participant in the http://drupalladder.org ladder for contributing to core. Please don't do anything with this post. The real issue has already been resolved in Drupal 8. If you would like to try this exercise yourself, visit http://drupalladder.org and click on Drupal Ladder
Current:
Optionally specify an alternative URL by which this content can be accessed. For example, type "about" when writing an about page. Use a relative path and don't add a trailing slash or the URL alias won't work.

Proposed:
The alternative URL for this content. For example, type "about" when creating an about page. Use a relative path without a trailing slash.