Restructure help dialog (#484)

- restructured help dialog
- moved isMac function to editor util
- added notice to CHANGELOG.md

Co-authored-by: Erik Michelson <github@erik.michelson.eu>
Co-authored-by: Tilman Vatteroth <tilman.vatteroth@tu-dortmund.de>
Co-authored-by: Renovate Bot <bot@renovateapp.com>
Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

src/components/editor/document-renderer-pane/document-render-pane.tsx

@@ -82,7 +82,7 @@ export const DocumentRenderPane: React.FC<DocumentRenderPaneProps & ScrollProps>
       ref={renderer} onScroll={userScroll} onMouseEnter={onMakeScrollSource} >
       <div className={'col-md'}/>
       <MarkdownRenderer
-        className={'flex-fill'}
+        className={'flex-fill mb-3'}
         content={content}
         wide={wide}
         onTocChange={(tocAst) => setTocAst(tocAst)}