Address privacy issue with start_url

[marcoscaceres]

Closes #399

This change (choose at least one, delete ones that don't apply):

• Adds new normative recommendations or optional items
• Makes editorial changes (changes informative sections, or changes normative sections without changing behavior)

Implementation commitment (delete if not making normative changes):

• This is an authoring requirement.

Commit message:
Attempt to address #399

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[marcoscaceres]

@npdoty, can you please take a look? Would this change satisfy PING?

[aarongustafson]

This looks good to me. Thanks @marcoscaceres!

[lknik]

@marcoscaceres Looks ok, "we're doing something" :)

[marcoscaceres]

Ok, let's take it and get more feedback before we go to CR as part of horizontal reviews.

[dmurph]

Adding myself as reviewer for searching purposes