Add metadata to trefoil example
* added metadata to trefoil
also updated link in the comment
* update trefoil metadata
* Update examples/plotting/trefoil.py
* Update examples/plotting/trefoil.py
+''' This example shows a Radiation Warning Symbol (Trefoil). It demonstrates
+rendering annular wegdes, different arrow heads and adding arc and segment
+glyphs.
+
+.. bokeh-example-metadata::
+ :apis: bokeh.plotting.Figure.annular_wedge, bokeh.plotting.Figure.arc, bokeh.plotting.Figure.segment, bokeh.models.TeeHead, bokeh.models.VeeHead
+ :refs: :ref:`userguide_annotations` > :ref:`userguide_annotations_arrows`, :ref:`userguide_styling` > :ref:`userguide_styling_adding_mathematical_notations`
+ :keywords: trefoil, teehead, veehead, arrow, arrow head, segment, arc, circle, annular wedge
+
+'''
from math import cos, radians, sin
from bokeh.core.properties import value
@@ -9,7 +19,7 @@ deg = lambda value: dict(value=value, units="deg")
cdot = "\u22c5"
degree = "\u00b0"
-# https://www.orau.org/ptp/articlesstories/radwarnsymbstory.htm
+# https://www.orau.org/health-physics-museum/articles/radiation-warning-symbol.html
def trefoil(R=1):
p = figure(
x_range=(-6*R, 6*R), y_range=(-6*R, 6*R),
