Improve contribute

[lxbarth]

The contribute ad shouldn't be The Hand of the Drowning but a simple banner or similar saying:

"Help us improve this guide"

linking to /contribute.

Draft text for /contribute:

Help us improve this guide

This guide is created and maintained by the OpenStreetMap and Humanitarian OpenStreetMap community. You can help us improve this guide by simply sending your feedback to or by contributing directly to it via GitHub.

Here are a couple of places where you can get started:

• Create a translation
• Improve language
• Fork and improve site

[jueyang]

implemented. Needs a little more styling.