docs(textarea): add known issue about interpolation in placeholder in IE

Closes #5025

Closes #14965

src/ng/directive/input.js

@@ -1778,6 +1778,20 @@ function checkboxInputType(scope, element, attr, ctrl, $sniffer, $browser, $filt
  * @param {string=} ngChange Angular expression to be executed when input changes due to user
  *    interaction with the input element.
  * @param {boolean=} [ngTrim=true] If set to false Angular will not automatically trim the input.
+ *
+ * @knownIssue
+ *
+ * When specifying the `placeholder` attribute of `<textarea>`, Internet Explorer will temporarily
+ * insert the placeholder value as the textarea's content. If the placeholder value contains
+ * interpolation (`{{ ... }}`), an error will be logged in the console when Angular tries to update
+ * the value of the by-then-removed text node. This doesn't affect the functionality of the
+ * textarea, but can be undesirable.
+ *
+ * You can work around this Internet Explorer issue by using `ng-attr-placeholder` instead of
+ * `placeholder` on textareas, whenever you need interpolation in the placeholder value. You can
+ * find more details on `ngAttr` in the
+ * [Interpolation](guide/interpolation#-ngattr-for-binding-to-arbitrary-attributes) section of the
+ * Developer Guide.
  */