Relax contribution guidelines

This MR lifts constraints on the description text to reduce the manual auditing effort.

Any manipulation of the unstructured description text is expensive in terms of manual auditing effort which makes version adjustments one of the most expensive tasks. We tried to automate it, but automated manipulation of natural text usually creates more problems than it solves.

However, the version information in the description usually does not hurt so that it is probably not worth to invest extra auditing time removing it.