Hints for yakuake in main

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• asv-description-first-para-too-short
  org.kde.yakuake.appdata.xml:107 - Yakuake is a drop-down terminal emulator based on KDE Konsole technology.
  The first `description/p` paragraph of this component might be too short (< 80 characters). Please consider starting with a longer paragraph to improve how the description looks like in software centers and to provide more detailed information on this component immediately in the first paragraph.