Update nl.yml

Lines 992-994: incorrect translation. IN this context "Map Key" should be translated by "Legende".
Line 1000: "Transport map" => "Transport Kaart"
Line 1000: typo in the word "kaart" (was "kaar")
Line 1033-1050: I don't know how to fix this but the NL strings don't fit in the space provided for the EN version, which creates a button mess. I suggest to arrange 3 buttons vertically.
Line 1042: "invoegen" is more appropriate than "opnemen"
Line 1002: there is no tooltip for the "Layers" feature. Correct tooltip would be "Kaartlagen".
Line 996: in the "base" section the "Humanitarian" map is not listed. Correct NL name would be "Humanitair".

Note: there are numerous tags which could have a better NL translation, but this is beyond the scope of this file change request. If you need help, let me know.