unified hoverlabel: update description

Author: antoinerg

src/components/fx/layout_attributes.js

@@ -61,6 +61,16 @@ module.exports = {
         editType: 'modebar',
         description: [
             'Determines the mode of hover interactions.',
+            'If `closest`, a single hoverlabel will appear',
+            'for the closest point within the `hoverdistance`.',
+            'If `x` (or `y`), multiple hoverlabels will appear for multiple points',
+            'at the closest `x`- (or `y`-) coordinate within the `hoverdistance`,',
+            'with the caveat that no more than one hoverlabel will appear per trace.',
+            'If `x unified` (or `y unified`), a single hoverlabel will appear',
+            'multiple points at the closest x- (or y-) coordinate within the `hoverdistance`',
+            'with the caveat that no more than one hoverlabel will appear per trace.',
+            'In this mode, spikelines are enabled by default perpendicular to the specified axis.',
+            'If false, hover interactions are disabled.',
             'If `clickmode` includes the *select* flag,',
             '`hovermode` defaults to *closest*.',
             'If `clickmode` lacks the *select* flag,',