Update fundraising counter footnote to explain running total and goal

[thibaudcolas]

Discussed during the January board meeting – update the text on the page to make clear that:

• The "$$$ donated" figure doesn’t include all donations or revenue sources.
• The $200,000 goal is a broad-strokes figure

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Code to change:

https://github.com/django/djangoproject.com/blob/f46f48b0a3c1e53cfe459e99152a8024858190ba/djangoproject/templates/fundraising/includes/donation_form_with_heart.html#L56C1-L59

Proposed new wording:

Your logo will be visible below if you contribute at least US $1,000. The running total represents donations made through this website only. The ${{ goal_amount|intcomma }} goal is a funding level set to provide financial sustainability to the project.