docs(dropdown): add note about usage with ngTouch

- Add note about an issue with the click event not bubbling up when
  using ng-click with ngTouch

Closes #5101
Closes #5189

src/dropdown/docs/readme.md

@@ -16,7 +16,7 @@ Each of these parts need to be used as attribute directives.
   * `always` - Automatically closes the dropdown when any of its elements is clicked.
   * `disabled` - Disables the auto close. You can control it manually with `is-open`. It still gets closed if the toggle is clicked, `esc` is pressed or another dropdown is open. It also won't be closed on `$locationchangeSuccess`.
   * `outsideClick` - Closes the dropdown automatically only when the user clicks any element outside the dropdown.
-  
+
 * `dropdown-append-to`
   <small class="badge">$</small>
   _(Default: `null`)_ -
@@ -32,24 +32,28 @@ Each of these parts need to be used as attribute directives.
   <i class="glyphicon glyphicon-eye-open"></i>
   _(Default: `false`)_ -
   Defines whether or not the dropdown-menu is open. The `uib-dropdown-toggle` will toggle this attribute on click.
-  
+
 * `keyboard-nav`:
   <small class="badge">B</small>
   _(Default: `false`)_ -
   Enables navigation of dropdown list elements with the arrow keys.
-  
+
 ### uib-dropdown-menu settings
 
 * `template-url`
   _(Default: `none`)_ -
   You may specify a template for the dropdown menu. Check the demos for an example.
-  
+
 ### Additional settings `uibDropdownConfig`
 
 * `appendToOpenClass`
   _(Default: `uib-dropdown-open`)_ -
   Class to apply when the dropdown is open and appended to a different DOM element.
-  
+
 * `openClass`
   _(Default: `open`)_ -
   Class to apply when the dropdown is open.
+
+### Known issues
+
+For usage with ngTouch, it is recommended to use the programmatic `is-open` trigger with ng-click - this is due to ngTouch decorating ng-click to prevent propagation of the event.