Merge branch '4.4' into 5.1

* 4.4:
  Added tip for files input rendering

Author: javiereguiluz

form/bootstrap4.rst

@@ -94,6 +94,13 @@ Checkboxes and Radios
 For a checkbox/radio field, calling ``form_label()`` doesn't render anything.
 Due to Bootstrap internals, the label is already rendered by ``form_widget()``.
 
+File inputs
+-----------
+
+File inputs are rendered using the Bootstrap "custom-file" class, which hides
+the name of the selected file. To fix that, use the `bs-custom-file-input`_
+JavaScript plugin, as recommended by `Bootstrap Forms documentation`_.
+
 Accessibility
 -------------
 
@@ -122,6 +129,8 @@ Symfony Form ``RadioType`` and ``CheckboxType`` by adding some classes to the la
     {{ form_row(form.myCheckbox, {label_attr: {class: 'switch-custom'} }) }}
 
 .. _`WCAG 2.0 standard`: https://www.w3.org/TR/WCAG20/
+.. _`bs-custom-file-input`: https://www.npmjs.com/package/bs-custom-file-input
+.. _`Bootstrap Forms documentation`: https://getbootstrap.com/docs/4.4/components/forms/#file-browser
 .. _`custom forms`: https://getbootstrap.com/docs/4.4/components/forms/#custom-forms
 .. _`custom radio`: https://getbootstrap.com/docs/4.4/components/forms/#radios
 .. _`custom checkbox`: https://getbootstrap.com/docs/4.4/components/forms/#checkboxes