[openstreetmap-website] Added links to the relevant OSMF sites and some additional text (#963)

[John Firebaugh]

An SVG can be found [here](https://github.com/osmlab/attribution-mark/blob/gh-pages/design/sprite.svg).

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Reply to this email directly or view it on GitHub:
https://github.com/openstreetmap/openstreetmap-website/pull/963#issuecomment-98562723
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