[Documentation] Add end-user's product logo guidelines

Along with migration to LFN, end user's product logo guidelines need to be defined. The guidelines can be copied over from [CNCF](https://github.com/cncf/landscape#logos) to [cnti certification repo](https://github.com/lfn-cnti/certification) or the [cnti main repo](https://github.com/lfn-cnti/cnti).

Adapt logo instruction reference at instructions.md
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