cubicweb-forge #676897 improve visibility of help menu ; add a simple howto [open]

The "help" on the lower part is wat too small to be seen by users. We also need simple howto and explanation of the terms used; for instance a user might not understand what 'story', 'bug' and 'cost' should exactly mean for him. When filling a ticket, we might for example like a visible help link to something like:

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