Update docs for Global Safe Fields

[skyqrose]

The docs instruct me to add fullStoryUrl to the global safe fields so it doesn't get scrubbed.

Two things that could be updated on the docs:

1. I guess the settings page has changed a bit since those docs were written, and the field is now in a "Data Scrubbing" section. Here's a screenshot:

2. As you can see in the screenshot, I don't have permission to edit that field in my organization. I assume setting it on the project-level, where someone is more likely to have edit permissions, would also satisfy the requirements. The docs could have saved me some time looking for a workaround if they had suggested that.