If you want to help out please join https://t.me/joinchat/BcFlFhFV4xmh1OCSj6xSpw and anounce what you want to port first.
See https://hig.kde.org/resources/contribute.html for information about git and sphinx.
Porting pages is quiet easy, there is an online converter for MediaWiki to reStructuredText http://pandoc.org/try/?text=&from=mediawiki&to=rst . You can copy the source of the original Wiki page there and convert it to rst. Download the images, add them to ./source/img/ and change the path in the rst. Most the time only links to other documents have to be adjusted.
The following pages are not yet ported:
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Concept
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Layout/ViewingVsEditing
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/ListView
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/TreeView
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/TabControl
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Tooltip
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/SearchPattern
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/EditingAndManipulation
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/DualList
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Grid
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/TextEdit
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Slider_and_Spin_Box
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Date_Time_Pickers
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/UserAssistance
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Callouts
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/MessageWidget
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/ProgressIndicator
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Messages
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Dialogs
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/HelpSystem
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Layout/Image
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Breadcrumbs
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Layout/Wizard
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Settings
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Organization
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Theme
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Color
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/BreezeDark
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/BreezeLight
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/BreezeHighContrast
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/IconDesign
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Animations
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Contractions
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Command_Link
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Buttons
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Toggle_Buttons
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Loading
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/RadioButtons
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/CheckBox
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/StatusBar
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/TableView
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/Toolbar
[ ] https://community.kde.org/KDE_Visual_Design_Group/HIG/About
[ ] https://community.kde.org/KDE_Visual_Design_Group/KirigamiHIG/Principles/OptimizedConverence
[ ] https://community.kde.org/KDE_Visual_Design_Group/KirigamiHIG/Principles/OneHandedUse