demo(tooltip): add tooltip-enable description, example

- Simple description about tooltip-enable.

- Add section demonstrating tooltip-enable

Closes #3372

Author: brunolellis

src/tooltip/docs/demo.html

@@ -31,5 +31,15 @@
         <label>Or use custom triggers, like focus: </label>
         <input type="text" value="Click me!" tooltip="See? Now click away..."  tooltip-trigger="focus" tooltip-placement="right" class="form-control" />
       </div>
+
+      <div class="form-group" ng-class="{'has-error' : !inputModel}">
+        <label>Disable tooltips conditionally:</label>
+        <input type="text" ng-model="inputModel" class="form-control"
+          placeholder="Hover over this for a tooltip until this is filled"
+          tooltip="Enter something in this input field to disable this tooltip"
+          tooltip-placement="top"
+          tooltip-trigger="mouseenter"
+          tooltip-enable="!inputModel" />
+      </div>
     </form>
 </div>

src/tooltip/docs/readme.md

@@ -16,6 +16,9 @@ will display:
 - `tooltip-popup-delay`: For how long should the user have to have the mouse
   over the element before the tooltip shows (in milliseconds)? Defaults to 0.
 - `tooltip-trigger`: What should trigger a show of the tooltip?
+  Note: this attribute is no longer observable. See `tooltip-enable`.
+- `tooltip-enable`: Is it enabled? It will enable or disable the configured
+  `tooltip-trigger`.
 - `tooltip-append-to-body`: Should the tooltip be appended to `$body` instead of
   the parent element?