Rewrite description for URL alias on node/add/*

Problem/Motivation

The help text for creating URL Aliases during node creation is confusing and wordy. This leads to users entering the wrong path.

Proposed resolution

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

Remaining tasks

A patch needs to be written changing the text.

User interface changes

Changes the help text on the node creation form.

API changes

No changes.

Original report by tanvish

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