Add 'n' shortcut for new doc

Fixed cmd+enter shortcut to publish doc
Fixed keyboard shortcut display on non-mac
Fixed heading alignment
Fixed documents smaller than page should not scroll

app/scenes/Document/components/Editor.js

@@ -48,6 +48,8 @@ class DocumentEditor extends React.Component<Props> {
 }
 
 const StyledEditor = styled(Editor)`
+  justify-content: start;
+
   p {
     ${Placeholder} {
       visibility: hidden;