Added metadata to bokeh\examples\plotting\checkout_form.py
* Added metadata to bokeh\examples\plotting\checkout_form.py
* Update examples/plotting/checkout_form.py
* Update refs
* Update examples/plotting/checkout_form.py
Did the required changes to 'refs' as per the suggestion.
+'''This example shows a sample checkout form created using bokeh widgets.
+
+.. bokeh-example-metadata::
+ :apis: bokeh.models.widgets.button, bokeh.models.widgets.checkbox, bokeh.models.widgets.groups, bokeh.models.widgets.inputs
+ :refs: :ref:`userguide_models_widgets`
+ :keywords: form, widgets, form, inputs
+
+'''
from bokeh.io import show
from bokeh.layouts import column, row
from bokeh.models.widgets import Button, Checkbox, RadioGroup, Select, TextInput
